Minimum bandwidth guarantee for input-buffered packet switch

ABSTRACT

A method and system for use in data communications. The method and system substantially ensure that actual data transmission per unit time from at least one input-buffered crossbar switch ingress to at least one input-buffered crossbar switch egress substantially satisfies a designated target amount of actual data transmission per unit time.

CROSS-REFERENCE

The present invention is related to subject matter disclosed in thefollowing co-pending application:

1. United States patent application Ser. No. 09/348,133 entitled,“Minimum Bandwidth Guarantee For Cross-Point Buffer Switch”, namingHiroshi Suzuki as the inventor, filed substantially contemporaneouslywith the present application and incorporated by reference herein in itsentirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is related to a method and system to be utilizedin data communications. In particular, the present invention is relatedto a method and system to be utilized in data communications involvingat least one data communications network.

2. Description of the Related Art

Data communications is the transfer of data from one or more sources toone or more sinks that is accomplished (a) via one or more data linksbetween the one more sources and the one or more sinks (b) according toa protocol. A data link is the means of connecting communicationsfacilities or equipment at one location to communications facilities orequipment at another location for the purpose of transmitting andreceiving data. A protocol, in communications, computer, dataprocessing, and control systems, is a set of formal conventions thatgovern the format and control the interactions between at least twocommunicating functional elements in order to achieve efficient andunderstandable communications. Examples of protocols are InternetProtocol (IP) and Asynchronous Transfer Mode (ATM) protocol.

A data communications network is the interconnection of three or morecommunicating entities (i.e., data sources and/or sinks) over one ormore data links. A data communications network connects and allowscommunication between multiple data sources and multiple data sinks overone or more data links. The concept of a data link includes the mediaconnecting the one or more data sources to one or more data sinks, aswell as the data communications equipment utilizing the media. The datacommunications networks utilize protocols to control the interactionsbetween data sources and sinks communicating over the one or more datalinks. Thus, it follows that such protocols must take into account thedata communications requirements of data sources and sinks desiringcommunication over the one or more data links.

Referring now to FIG. 1, shown is a partially-schematic diagram of arelated art data communications network. Depicted are six datasources/sinks: data source/sink A 100, data source/sink B 102, datasource/sink C 104, data source/sink D 106, data source/sink E 108, anddata source/sink F 110. The depicted six data sources/sinks areconnected by/through data communications network 112. Illustrated isthat data communications network 112 is composed of numerous datacommunications links 150-184 and network nodes 116-128. Shown is thatwithin each network node 116-128 resides crossbar switches 130-142,respectively.

Historically, each crossbar switch 130-142, was a switch that had anumber of vertical paths, a number of horizontal paths, andelectromagnetic-operated mechanical devices, i.e., electromechanicalrelays, for interconnecting any one of the vertical paths with any oneof the horizontal paths. (While the foregoing is historically truththose skilled in the art will recognize that the logical functions ofcrossbar switches are generally performed using combinational circuits;however, the term “crossbar” switch has been retained for suchcombinational circuits even though such circuits typically no longeractually utilize a true physical “crossbar.”) Thus, theelectromagnetic-operated mechanical devices within each crossbar switch130-142 can be utilized to interconnect at least one data communicationslink on one side of any particular crossbar switch to at least one datacommunications link on the other side of the particular crossbar switch.For example, crossbar switch 130 internal to network node 116 containscircuitry sufficient to connect any one of data communications links150-154 with any one of data communications links 156-162. Likewise,crossbar switch 136 internal to network node 122 contains circuitrysufficient to connect any one of data communications link 163, 166, 170with any one of data communications links 174-176. The same holds truefor the other crossbar switches depicted in FIG. 1.

When data communications is desired between any two data sources/sinks(e.g., data source/sink A 100 with data source/sink D 106, datasource/sink B 102 with data source/sink F 100, or data source/sink C 104with data source/sink E 108) appropriate crossbar switches 130-142 canbe utilized to establish hardwire paths between the data source/sinkpair. At present, there are two basic ways in which a crossbar switches130-142 can be utilized to establish a communications path through datacommunications network 112: (1) by use of what is known in the art as“circuit switching”; and (2) by use of what is known in the art as“packet switching.” The present invention is related to crossbarswitches in packet-switched networks. However, before packet-switchednetworks are discussed, the functioning of crossbar switches in acircuit-switched network is discussed because discussing the functioningof crossbar switches in a circuit switched network serves as a goodintroduction to discussing the functioning of crossbar switches inpacket-switched networks.

Referring now to FIG. 2, shown are three “circuit switched” paths whichare used to introduce the functioning of crossbar switches. In what isknown in the art as “circuit switching,” an actual physical circuit isestablished between each data source/sink pair. Depicted in FIG. 2 iscircuit switched path 1 connecting data source/sink A 100 with datasource/sink D 106. Illustrated is that circuit switched path 1 iscomposed of data communications link 150-network node 116-datacommunications link 162-network node 126-data communications link178-network node 124-data communications link 170-network node 122-datacommunications link 174. With respect to circuit switched path 1, shownis that crossbar switch 130 connects data communications link 150 withdata communications link 162, crossbar switch 140 connects datacommunications link 162 with data communications link 178, crossbarswitch 138 connects data communications link 178 with datacommunications link 170, crossbar switch 136 connects datacommunications link 170 with data communications link 174. Also depictedis circuit switched path 2 connecting data source/sink B 102 with datasource/sink F 110. Circuit switched path 2, and each of the depictedcomponents making up circuit switched path 2, functions in a mannersimilar to that described in relation circuit switched path 1. Furtherdepicted is circuit switched path 3 connecting data source/sink C 104with data source/sink E 108. Circuit switched path 3, and each of thedepicted components making up circuit switched path 3, also functions ina manner similar to that described in relation circuit switched path 1.

Referring now to FIG. 3, shown is the use of “packet switching” totransmit data through data network 112, and how crossbar switches areutilized in a packet-switched network. In what is known in the art as“packet switching,” data to be transmitted between each data source/sinkpair is encapsulated in a “packet” which, in data communications, is asequence of binary digits that (a) includes data, control signals, andpossibly error control signals, and (b) is arranged in a specificformat, such as a header part and data part, wherein the header partgenerally contains information indicative of the source and destinationof the data part of the packet (thus, as used, the term “packet”includes all such unitized data, such as, for example IP packets or ATMcells. Whereas in circuit switching, crossbar switches 130-142 werekeyed to and switched, or controlled, upon the basis of a circuit to beestablished throughout data communications network 112 throughout theduration of a call, in “packet switching” crossbar switches 130-142 arekeyed to, and switched upon, the basis of header information (e.g., thesource and destination information contained within the header). Thatis, each crossbar switch 130-142 typically has some intelligencesufficient to (1) “read” the source and destination information of apacket received into the crossbar switch from a data communications linkserving as input to the crossbar switch, (2) on the basis of such readsource and destination information determine the appropriate datacommunications link to serve as output from the crossbar switch, (3)establish a connection between the input data communications link andoutput data communications link, and (4) thereafter transmit the packetacross a switch.

Depicted in FIG. 3 are packets 300-316. Illustrated is that packets300-304 contain data originating at data source/sink A 100 and destinedfor data source/sink data source/sink D 106, a fact reflected in theheaders of packets 300-304. In addition, shown is that the headers ofpackets 300-304 are also numbered relative to each other, so that thepackets can be placed in their appropriate order upon receipt at datasource/sink D 106. Illustrated is that packets 306-310 contain dataoriginating at data source/sink B 102 and destined for data source/sinkdata source/sink E 108, a fact reflected in the headers of packets306-310. In addition, shown is that the headers of packets 306-310 arealso numbered relative to each other, so that the packets can be placedin their appropriate order upon receipt at data source/sink E 108.Illustrated is that packets 312-314 contain some data originating atdata source/sink C 104 and destined for data source/sink D 106, somedata originating at data source/sink C 104 and destined for datasource/sink E 108, some data originating at data source/sink C 104 anddestined for data source/sink F 110, a fact reflected in the headers ofpackets 312-316.

Inspection of data communications network 112 shows that there aremultiple paths through data communications network 112 from any datasource/sink A 100, data source/sink B 102, or data source/sink C 104, toany data source/sink D 106, data source/sink E 108, or data source/sinkF 110. Since packet switching is being utilized, each crossbar switch130-142 is rapidly switching between various inputs and outputs inresponse to the source and destination information in each packetreceived on each input of each such crossbar switch 130-142. This rapidswitching is illustrated by the dashed lines connecting the datacommunications links on either side of the crossbar switches 130-142.

Those skilled in the art will recognize that there are two basic ways inwhich packets are transmitted through a packet switched network: thedatagram method and the virtual circuit method. In the datagram method,each packet is treated independently. That is, each network node 116-128makes an independent routing decision for each packet received,irrespective of similarly addressed packets previously received.Consequently, it is likely that packets, even if they have the samedestination address, will not all follow the same route through datacommunications network 112, and thus it will be up to the destinationdata source/sink to reassemble the packets in the correct order uponreceipt. In the virtual circuit approach, a fixed route from aparticular data source/sink to a particular data source/sink, throughdesignated network nodes of data communications network 112, isestablished prior to any packets are sent. Thereafter, all packets fromthe particular data source/sink to the particular data source/sink willfollow the fixed route through data communications network 112 therebyensuring that any packets so transmitted arrive at the destination datasource/sink in the order in which such packets were transmitted.

In the early days of data communications networks, circuit switching wasused for data communications requiring near continuous transmission andreception (e.g. full motion video and/or continuous audio), while packetswitching which used for virtually all other types of data. However, inmore recent times a move has been made in the industry to utilize packetswitching, even for data communications traditionally thought to requirenear continuous transmission and reception. Examples of this areseemingly continuous voice and data over Internet Protocol (IP) orAsynchronous Transfer Mode (ATM) networks. This is achieved by adigitizing, segmenting, packetizing, transmitting, unpacketizing,re-assembling, and displaying the data at a speed sufficient such thathuman perception cannot detect discontinuity in the data.

As packets transit data communications network 112, it is possible andindeed likely that multiple packets will converge upon a particularnetwork node substantially simultaneously and/or in rapid succession. Anillustration of such an event is depicted in FIG. 4, wherein is shownnetwork node 122 containing crossbar switch 136. Depicted is that ninepackets which were illustrated in FIG. 3 as being generated by datasources/sinks A 100, B 102, and C 104 are converging upon network node122. Notice that two of the first packets that will be received bynetwork node 122, at what will be assumed to be substantially the sametime, are both directed to data source/sink 106 (e.g., packet 304 and312) which resides on data communications link 174. Packet 304 arrivesat network node 122 via data communications link 166 while packet 312arrives at network node 122 via data communications link 170 atsubstantially same time.

As those skilled in the art will appreciate, by its nature crossbarswitch 136 can only connect one data communications link to datacommunications link 174 at any particular instant in time. Thus, one orthe other of data packets 304 and 312 will have to wait, typically in abuffer, depending upon which of data packets 304 and 312 crossbar switch136 decides to transmit first.

In the early days of packet switched networks, the fact that datapackets might have to wait for transmission at a particular network nodedid not pose that great of a problem, and such delays were in the maintolerated. However, the use of packet switching for such datacommunications requiring near continuous transmission and reception hasgiven rise to a need to be able to schedule which packets will have towait, and which will be directly transmitted through a particular nodeby a particular crossbar switch, since it is critical that such traffic(network traffic consisting of data requiring near continuoustransmission reception, such as full motion video and/or audio)experience substantially minimal delays at network nodes as such traffictransits data communications network 112.

The need for scheduling packets through a particular crossbar switchthat is resident within a particular network node has been met by thecreation of what are known in the art as “schedulers”. These schedulersuse a variety of different schemes to ensure that data packetsdesignated as having “high” or “higher” priority, relative to other datapackets waiting for transmission through a particular crossbar switch,are transmitted prior to data packets having relatively “low” or “lower”priority.

Schedulers in existence do a passable job of ensuring that therelatively “high” or “higher” data packets transit particular crossbarswitches relatively efficiently. However, recall from the discussionabove that other traffic exists on data communications network 112which, although of a “low” or “lower” priority, still needs to transitdata communications network 112. Unfortunately, virtually all schedulersin existence focus on assuring that the relatively “high” or “higher”priority data packets transit particular crossbar switches in anefficient manner, and then rely on network “slack,” or a momentarydecrease in data traffic loading at the particular crossbar switches toallow the transmission of the relatively a “low” or “lower” prioritydata packets through the particular crossbar switches.

The foregoing referenced scheduler schemes initially worked relativelywell. However, increasing data communications network traffic has madeit more and more likely that insufficient slack will manifest itselfwithin the network sufficient to allow the transmission of the low orlower priority data packets through the particular crossbar switches.The result of this is typically buffer (temporary packet storageavailable within circuitry substantially proximate to the associatedparticular crossbar switch, such circuitry being known in the art as thecrossbar “switch fabric”) overloading and subsequent loss of data at theparticular crossbar switches. The inability to transmit such low orlower priority data packets through one or more particular crossbarswitches is known in the art as “starving” the low or lower prioritydata packets by denying them network bandwidth necessary for them toremain in existence.

Those skilled in the art will recognize that although certain datapackets have been designated to be of a relatively low or lower priorityin a data network communications sense, such data is still important tothe persons from whom and to whom it is directed. Accordingly, it isapparent that a need exists in the art for a method and system whichwill substantially alleviate the starving of relatively low or lowerpriority data packets while substantially insuring that relatively highor higher priority data packets transit a particular crossbar switchwith relatively low delay.

SUMMARY OF THE INVENTION

It has been discovered that a method and system can be achieved whichwill substantially alleviate the starving of relatively low or lowerpriority data packets at a particular crossbar switch within a datacommunications network while substantially ensuring that relatively highor higher priority data packets transit that same particular crossbarswitch with relatively low delay. The method and system substantiallyensure that actual data transmission per unit time from at least oneinput-buffered crossbar switch ingress to at least one input-bufferedcrossbar switch egress substantially satisfies a designated targetamount of actual data transmission per unit time.

The foregoing is a summary and thus contains, by necessity,simplifications, generalizations and omissions of detail; consequently,those skilled in the art will appreciate that the summary isillustrative only and is not intended to be in any way limiting. Otheraspects, inventive features, and advantages of the present invention, asdefined solely by the claims, will become apparent in the non-limitingdetailed description set forth below.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention may be better understood, and its numerousobjects, features, and advantages made apparent to those skilled in theart by referencing the accompanying drawings.

FIG. 1 shows a partially-schematic diagram of a related art datacommunications network.

FIG. 2 shows three “circuit switched” paths which are used to introducethe functioning of crossbar switches.

FIG. 3 shows the use of “packet switching” to transmit data through datanetwork 112, and how crossbar switches are utilized in a packet-switchednetwork.

FIG. 4 shows network node 122 containing crossbar switch 136.

FIG. 5 shows an expanded view of crossbar switch 136 contained withinnetwork node 122.

FIG. 6 shows a high-level partially schematic block diagram depicting anembodiment of the present invention in the context of an input queuedswitch where each ingress-egress pair has a queue which can be accessedindependently of, and simultaneously with, other queues associated withother ingress-egress pairs.

FIG. 7 depicts a high-level logic flowchart which illustrates thecontrol of the values of bandwidth counters for Ingress_1 500, Ingress_2502, and Ingress_3 504.

FIG. 8A shows a high-level logic flowchart illustrating a process whichcan be utilized by excess bandwidth scheduler for Egress_1 600 andguaranteed minimum bandwidth scheduler for Egress_1 602.

FIG. 8B1 depicts a high-level logic flowchart showing an embodiment of aprocess, referenced in method step 809 of FIG. 8A, whereby a packet istransmitted under the control of guaranteed minimum bandwidth schedulerfor Egress_1 602.

FIG. 8B2 depicts a high-level logic flowchart illustrating an embodimentof a process, referenced in method step 813, utilized to update pointerPE1.

FIG. 8C1 depicts a high-level logic flowchart showing an embodiment of aprocess, referenced in method step 811 of FIG. 8A, whereby a packet istransmitted under the control of excess bandwidth scheduler for Egress_1600.

FIG. 8C2 depicts a high-level logic flowchart illustrating an embodimentof a process, referenced in method step 823, utilized to update pointerPEB1.

FIG. 9 shows a high-level partially schematic block diagram depicting anembodiment of the present invention in the context of an input queuedswitch where each ingress-egress pair has a queue which can be accessedindependently of, and simultaneously with, other queues associated withother ingress-egress pairs.

FIG. 10 depicts a high-level logic flowchart which illustrates thecontrol of the values of bandwidth counters for Ingress_1 500, Ingress_2502, and Ingress_3 504.

FIG. 11A shows a high-level logic flowchart illustrating a process whichcan be utilized by excess bandwidth scheduler for Egress_2 604 andguaranteed minimum bandwidth scheduler for Egress_2 606.

FIG. 11B1 depicts a high-level logic flowchart showing an embodiment ofa process, referenced in method step 1109 of FIG. 11A, whereby a packetis transmitted under the control of guaranteed minimum bandwidthscheduler for Egress_2 606.

FIG. 11B2 depicts a high-level logic flowchart illustrating anembodiment of a process, referenced in method step 1113, utilized toupdate pointer PE2.

FIG. 11C1 depicts a high-level logic flowchart showing an embodiment ofa process, referenced in method step 1111 of FIG. 11A, whereby a packetis transmitted under the control of excess bandwidth scheduler forEgress_2 604.

FIG. 11C2 depicts a high-level logic flowchart illustrating anembodiment of a process, referenced in method step 1123, utilized toupdate pointer PEB2.

FIG. 12 shows a high-level partially schematic block diagram depictingan embodiment of the present invention in the context of an input queuedswitch where each ingress-egress pair has a queue which can be accessedindependently of, and simultaneously with, other queues associated withother ingress-egress pairs.

FIG. 13 depicts a high-level logic flowchart which illustrates thecontrol of the values of bandwidth counters for Ingress_1 1201,Ingress_2 1203, and Ingress_M 1205. Method step 1300 shows the start ofthe process.

FIG. 14A shows a high-level logic flowchart illustrating a process whichcan be utilized by excess bandwidth scheduler for Egress_N 1204 andguaranteed minimum bandwidth scheduler for Egress_N 1206.

FIG. 14B1 depicts a high-level logic flowchart showing an embodiment ofa process, referenced in method step 1409 of FIG. 14A, whereby a packetis transmitted under the control of guaranteed minimum bandwidthscheduler for Egress_N 1206.

FIG. 14B2 depicts a high-level logic flowchart illustrating anembodiment of a process, referenced in method step 1413, utilized toupdate pointer PE_N.

FIG. 14C1 depicts a high-level logic flowchart showing an embodiment ofa process, referenced in method step 1411 of FIG. 14A, whereby a packetis transmitted under the control of excess bandwidth scheduler forEgress_N 1204.

FIG. 14C2 depicts a high-level logic flowchart illustrating anembodiment of a process, referenced in method step 1423, utilized toupdate pointer PEB_N.

FIGS. 15 and 16 show a pictographic representations of the “minimumbandwidth guarantee for crossbar switches having input queues” schemeemployed within a crossbar switch having non-independently accessibleinput buffers environment (hereinafter, for sake of brevity, a crossbarswitch having non-independently accessible input buffers will bereferred to as an “input-buffered crossbar switch”).

FIG. 17 shows an example of cross-point buffer switch 1700 responding toa particular state of events illustrated in pending packets requestingtransmission diagram 1702.

FIG. 18 depicts an example of a crossbar switch 1800, having one inputbuffer 1801 per each ingress of crossbar switch 1800, where each switchingress has associated with it a number of “queues”.

FIG. 19 shows a high-level logic flowchart illustrating a process whichcan be utilized with cross bar switches having input buffers.

FIG. 20 shows an example of a “packet transmit by contention resolutionand transmit packet scheduler” process. The use of the same referencesymbols in different drawings indicates similar or identical items.

FIG. 21 shows an example of the “schedulers (one at each egress) utilizeguaranteed minimum bandwidth and excess bandwidth constraints to resolveany contentions arising from more than one queue at the same ingressvying for access to an egress, and build Candidate Ingress Queue-EgressPhysical Connections Matrix for each egress” process referenced inmethod step 2000.

FIG. 22 depicts an example of the “no candidate packet selected” processreferenced in method step 2106.

FIG. 23 illustrates an example of the “Select a Candidate for Egress_eTaking Into Account Minimum Bandwidth Scheduler Constraints” processreferenced in method step 2110.

FIG. 24 shows an example of the “update value held within pointer PE_e”process referenced in method step 2302.

FIG. 25 depicts an example of the “Select a Candidate for Egress_eTaking Into Account Excess Bandwidth Scheduler Constraints” processreferenced in method step 2112.

FIG. 26 shows an example of the “update value held within PEB_e” processreferenced in method step 2502.

FIG. 27 shows an example of the “ingress queue-egress connectionschedulers (one at each egress) utilize Candidate Ingress Queue-EgressPhysical Connections Matrix, resolve any contentions arising from morethan one egress scheduled to connect to the same ingress, and buildGranted Ingress Queue-Egress Physical Connections Matrix for eachegress” process referenced in method step 2002.

FIG. 28 shows an example of the “update value held within PI_i” processreferenced in method steps 2714 and 2710.

FIG. 29 shows an example of the “transmission units (one at eachegress), utilizing Granted Ingress Queue-Egress Physical ConnectionsMatrix, transmit packets adjusting bandwidth counters as appropriate”process referenced in method step 2004.

The use of the same reference symbols in different drawings indicatessimilar or identical items.

DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

The following sets forth a detailed description of the best contemplatedmode for carrying out the invention as described in the claims. Thedetailed description is intended to be illustrative and should not betaken as limiting.

With reference to the figures, and in particular with reference now toFIG. 5, shown is an expanded view of crossbar switch 136 containedwithin network node 122. Depicted is that respectively associated withswitch ingresses 500-504 into crossbar switch 136 are lookup tablemappers 506-510, which map each received data packet to its appropriateswitch egress 512-514 dependent upon information contained within theheader of each such received data packet in a fashion well-known tothose having ordinary scale on the art.

Switch egresses 512-514 respectively connect with data communicationslinks 174-176. As has been discussed, it is possible that multiplepackets, destined for the same data communications link, will arrive atsubstantially the same time at network node 122. So that data is notlost while a preceding packet is transmitted over the desired datacommunications link, a queue is often associated with eachingress-egress pair within a particular crossbar switch such that onemore packets can be stored while waiting to be transmitted over thecurrently-in-use data communications link. Examples of queues areillustrated in FIG. 5 as ingress-egress queues 516-526, each of which isshown respectively connected between its associated particularingress-egress pair.

Since it is possible that more than one ingress-egress queue 516-526will have data waiting for transmission over the same egress, it isnecessary to schedule the order in which ingress-egress queues 516-526associated with a particular egress will be serviced. This function istypically handled by schedulers 528-530.

Most modern scheduler schemes in packet switched networks use some typeof crossbar switch scheme which ensures that higher priority datapackets get passed through the crossbar switch, and lets the lowerpriority data packets fend for themselves. With respect to those schemeswhich do try to ensure that some of the lower priority data packets getserviced, the basic idea of such schemes is that eventually a break inthe higher priority traffic will allow the lower priority traffic to beserviced.

Although from a bandwidth conservation viewpoint, higher priority datais more “important,” in human user terms, even lower priority data canbe very important. The processes and devices described below both ensurethat a substantial portion of the lower priority data gets through acrossbar switch and preserve the ability of the switch to service higherpriority data.

The processes and devices described below go completely against theconventional wisdom and, at least initially, ignore the priority of thepackets transiting a switch. Instead, the processes and devices ensurethat each ingress is allowed an equal share of some defined targetminimum actual data transmission per unit time between each particularingress and each particular egress of a switch. Thus, the processes anddevices insure that even ingresses having lower priority data will beserviced on a regular basis, thereby decreasing the amount oflow-priority traffic dropped due to buffer overfill.

While the processes and devices described do take away some bandwidthfrom higher priority traffic, and thus seem counterintuitive, in mostinstances the benefits achieved from decreasing data loss (e.g.,decreased requests for retransmission, decreased network trafficassociated with the decreased requests for retransmission, decreaseddelay in supplying communications to lower priority users, etc.)outweigh the cost (a practicably negligible decrease in bandwidthavailable to the higher priority traffic). In addition, since the targetcan be adjusted, a system administrator can adjust the parametersassociated with the processes and devices described below until thesystem administrator gets a good balance between serving lower prioritytraffic and serving higher priority traffic.

The processes and devices described below utilize a “minimum bandwidthguarantee for crossbar switches having input queues” scheme that doesthe foregoing by controlling access of all ingress queues to aparticular egress by examining two quantities, W_(ij) and Q_(ij), intandem. W_(ij) is an invented quantity, which is termed a “bandwidthcounter,” and which represents the relationship between (a) actual datatransmission per unit time from an Ingress i to an Egress j and (b) atarget minimum amount of actual data transmission per unit time from theIngress i to the Egress j. Q_(ij) is the number of packets in a queueinterposed between the Ingress i and the Egress j. The scheme is that ifa particular ingress, represented by Q_(ij), (a) has data waiting to betransmitted, and (b) also has a bandwidth counter which indicates thatIngress i has actual data transmission per unit time from Ingress i toEgress j less than Ingress i's target minimum amount of actual datatransmission per unit time from Ingress i to Egress j, then Ingress i(or it's associated queue Q_(ij)) will be given access to Egress jbefore any other ingresses (or queues) which fail to meet such dualcriteria.

In addition, the scheme will release control of access to an Egress j toother access control methods when either (a) all target minimum actualdata transmissions per unit time for the ingresses feeding the Egress jhave been met, or (b) queues having unmet targets have no data totransmit to Egress j.

Subsequent to data transmission from an Ingress i to an Egress j, abandwidth counter W_(ij), is adjusted by a factor dependent upon theamount of data transmitted.

Simultaneous with all the foregoing taking place, a clocked process runsin the background, which, upon the expiration of a defined unit of time,reinitializes all W_(ij), or all bandwidth counters, so that the targetsper unit time for all ingress-egress pairs are always current.

The “minimum bandwidth guarantee for crossbar switches having inputqueues” scheme as described works particularly well for an input queuedcrossbar switches where each ingress-egress pair has a queue which canbe accessed independently of, and simultaneously with, other queuesassociated with other ingress-egress pairs. However, when an attempt ismade to apply the “minimum bandwidth guarantee for crossbar switcheshaving input queues” scheme to input queued crossbar switches where eachingress-egress pair has a queue which cannot be accessed independentlyof, and simultaneously with, other queues associated with otheringress-egress pairs several problems arise which should be overcome inorder to allow the scheme to function with such switches in the mostoptimum fashion. Utilization of the scheme in these different types ofswitches is discussed in turn below.

I. Cross-Point Buffer Switch

Referring now to FIG. 6, shown is a high-level partially schematic blockdiagram depicting an embodiment of the present invention in the contextof an input queued switch where each ingress-egress pair has a queuewhich can be accessed independently of, and simultaneously with, otherqueues associated with other ingress-egress pairs. As used herein, thedefined term for such a switch is “cross-point buffer switch,” a termwhich arises from viewing the switch as an old-style crossbar switch inwhich each ingress-egress connection is actually established by crossingtwo metallic bars at a particular point in space (the “crosspoint”);when the switch is so viewed, each buffer associated with a particularingress-egress pair can likewise be viewed as being associated with the“cross-point” creating the ingress-egress connection. Hence the term,“cross-point buffer switch.”

Illustrated is that both switch egress_1 512 and switch egress_2 514have respectively associated with them (1) excess bandwidth schedulers600, 604, and (2) guaranteed minimum bandwidth schedulers 602, 606. Eachguaranteed minimum bandwidth scheduler for each egress assures that eachqueue, and consequently each ingress associated with each queue, isgiven some “guaranteed,” or target, minimum data transmission per unittime (as used herein the term “guaranteed” means essentially a targetwhich will be satisfied if the physical constraints of a switch allow)via the guaranteed minimum bandwidth scheduler's egress, irrespective ofthe priority of the packets that might be resident within each queue.This substantially ensures that no switch ingress is ever completely“starved” of bandwidth, even if the only packets resident within aparticular queue associated with a switch ingress are packets of thelowest possible priority. In the event that no queue requesting datatransmission has an unmet guaranteed minimum data transmission per unittime, the excess bandwidth scheduler for the egress assigns suchbandwidth over and above that bandwidth constituting guaranteed minimumbandwidth to the queues associated with the egress in a fair manner. Itis to be understood that, in at least one embodiment, when utilized witha cross-point buffer switch, the guaranteed minimum bandwidth schedulerand excess bandwidth scheduler at each egress functions substantiallyindependent of guaranteed minimum bandwidth schedulers and excessbandwidth schedulers at resident at other egresses.

Depicted as associated with switch egress_1 512 is guaranteed minimumbandwidth scheduler for egress_1 602 and excess bandwidth scheduler foregress_1 600. As discussed, guaranteed minimum bandwidth scheduler foregress_1 602 is keyed to a guaranteed minimum bandwidth associated witheach switch ingress 500-504. The guaranteed minimum bandwidth isrepresented by a bandwidth counter, associated with each particularswitch ingress 500-504, which is indicative of a relationship between(a) an amount of actual data transmitted, during a prescribed unit oftime T, from each particular switch ingress 500-504 to switch egress_1512 and (b) a target minimum amount of actual data transmission fromeach particular switch ingress 500-504 to switch egress 512. Thesebandwidth counters are represented in FIG. 6 as W_(Ingress) _(—) ₁ _(—)_(for) _(—) _(Egress) _(—) ₁ 608, W_(Ingress) _(—) ₂ _(—) _(for) _(—)_(Egress) _(—) ₁ 610, and W_(Ingress) _(—) ₃ _(—) _(for) _(—) _(Egress)_(—) ₁ 612.

With reference now to FIG. 7, depicted is a high-level logic flowchartwhich illustrates the control of the values of bandwidth counters forIngress_1 500, Ingress_2 502, and Ingress_3 504. Method step 700 showsthe start of the process. Method step 702 depicts thatEgress_1_Countdown_Timer is initialized to Time_Interval_(for)_Egress_1.Method step 704 illustrates that W_(Ingress) _(—) ₁ _(—) _(for) _(—)_(Egress) _(—) ₁ 608, W_(Ingress) _(—) ₂ _(—) _(for) _(—) _(Egress) _(—)₁ 610, and W_(Ingress) _(—) ₃ _(—) _(for) _(—) _(Egress) _(—) ₁ 612 areeach set to values indicative of the minimum data transmissionguaranteed to their respective ingresses during theTime_Interval_for_Egress_1. Method step 706 illustrates thatEgress_1_Countdown_Timer is started and begins to countdown by somepredetermined amount of time decrement (the actual amount of decrementis a design choice). Method step 708 shows the determination of whetherEgress_1_Countdown_Timer has counted down to be equal to zero. In theevent that Egress_1_Countdown_Timer is greater than zero, the processloops to method step 708. In the event that Egress_1_Countdown Timer isless than or equal to zero, the process returns to method step 702 andexecutes from that point. Thus, as can be seen, the high-level logicflowchart of FIG. 7 ensures that W_(Ingress) _(—) ₁ _(—) _(for) _(—)_(Egress) _(—) ₁ 608, W_(Ingress) _(—) ₂ _(—) _(for) _(—) _(Egress) _(—)₁ 610, and W_(Ingress) _(—) ₃ _(—) _(for) _(—) _(Egress) _(—) ₁ 612 areeach reset to values indicative of the minimum bandwidth guaranteed totheir respective ingresses at the start of every successiveTime_Interval_for_Egress_1.

It is to be understood that the process illustrated in FIG. 7 is to berunning simultaneously with the process which will now be shown in FIGS.8A, 8B1, 8B2, 8C1, and 8C2. The process illustrated in FIG. 7 ensuresthat W_(Ingress) _(—) ₁ _(—) _(for) _(—) _(Egress) _(—) ₁ 608,W_(Ingress) _(—) ₂ _(—) _(for) _(—) _(Egress) _(—) ₁ 610, andW_(Ingress) _(—) ₃ _(—) _(for) _(—) _(Egress) _(—) ₁ 612 are reset totheir predetermined values after the elapsing of everyTime_Interval_for_Egress_1 period of time. The process shown in FIGS.8A, 8B1, 8B2, 8C1, and 8C2 depicts how W_(Ingress) _(—) ₁ _(—) _(for)_(—) _(Egress) _(—) ₁ 608, W_(Ingress) _(—) ₂ _(—) _(for) _(—) _(Egress)_(—) ₁ 610, and W_(Ingress) _(—) ₃ _(—) _(for) _(—) _(Egress) _(—) ₁ 612can be utilized to substantially ensure that none of Ingress_1 500,Ingress_2 502, or Ingress_3 504 is being starved of Egress_1 512bandwidth.

Referring now to FIG. 8A, shown is a high-level logic flowchartillustrating a process which can be utilized by excess bandwidthscheduler for Egress_1 600 and guaranteed minimum bandwidth schedulerfor Egress_1 602. Method step 800 shows the start of the process. Methodstep 801 depicts that (1) a pointer, “PE1”, used by guaranteed minimumbandwidth scheduler for Egress_1 602 in the manner set forth below, isinitialized to be equal to one; and (2) a pointer, “PEB1”, used byexcess bandwidth scheduler for Egress_1 600 in the manner set forthbelow, is initialized to be equal to one.

Method step 803 illustrates the inquiry as to whether at least one ofIngress_1-Egress_1 queue 516, or Ingress_2-Egress_1 queue 520, orIngress_3-Egress_1 queue 524 feeding Egress_1 512 has a packet waitingfor transmission. In the event that the inquiry shown in method step 803finds that none of Ingress_1-Egress_1 queue 516, or Ingress_2-Egress_1queue 520, or Ingress_3-Egress_1 queue 524 feeding Egress_1 512 has apacket waiting for transmission, the process proceeds to method step 805which depicts that no packet is sent. Thereafter, the process proceedsto method step 803 and executes from that point.

In the event that the inquiry shown in method step 803 finds that atleast one of Ingress_1-Egress_1 queue 516, or Ingress_2-Egress_1 queue520, or Ingress_3-Egress_1 queue 524 feeding Egress_1 512 has a packetwaiting for transmission, the process proceeds to method step 807 whichdepicts an embodiment of an inquiry as to whether any one or more queueswhich have a packet waiting for transmission also have a non-zerobandwidth counter; method step 807 shows that in one embodiment theinquiry is accomplished by checking whether any one of the followingconditions is met:

Is W_(Ingress) _(—) ₁ _(—) _(for) _(—) _(Egress) _(—) ₁ 608 greater thanzero and is at least one packet resident at Ingress_1-Egress_1 queue516? or

Is W_(Ingress) _(—) ₂ _(—) _(for) _(—) _(Egress) _(—) ₁ 610 greater thanzero and is at least one packet resident at Ingress_2-Egress_1 queue520? or

Is W_(Ingress) _(—) ₃ _(—) _(for) _(—) _(Egress) _(—) ₁ 612 greater thanzero and at least one packet is resident at Ingress_3-Egress_1 queue524?

In the event that any one of the foregoing conditions is true, theprocess proceeds to method step 809 which depicts the transmission of apacket under the control of guaranteed minimum bandwidth scheduler forEgress_1 602 utilizing a process, an embodiment of which is described inFIGS. 8B1 and 8B2, below. In the event that none of the foregoingconditions of method step 807 is true, the process proceeds to methodstep 811 which depicts the transmission of a packet under the control ofexcess bandwidth scheduler for Egress_1 600, an embodiment of which isdescribed in FIGS. 8C1 and 8C2, below. Subsequent to the performance ofeither method step 809 or 811 the process loops back to method step 803and continues from that point.

With reference now to FIG. 8B1, depicted is a high-level logic flowchartshowing an embodiment of a process, referenced in method step 809 ofFIG. 8A, whereby a packet is transmitted under the control of guaranteedminimum bandwidth scheduler for Egress_1 602. Method step 809A depictsthe start of the “packet transmit under the control of minimum bandwidthscheduler” process. Method step 806 depicts the inquiry of whetherW_(Ingress) _(—) _((PE1)) _(—) _(for) _(—) _(Egress) _(—) ₁ (e.g.,W_(Ingress) _(—) _((PE1)) _(—) _(for) _(—) _(Egress) _(—) ₁ would equateto W_(Ingress) _(—) ₁ _(—) _(for) _(—) _(Egress) _(—) ₁ if PE1 was equalto one, W_(Ingress) _(—) ₂ _(—) _(for) _(—) _(Egress) _(—) ₁ if PE1 wasequal to two, etc.) is greater than zero.

In the event that the inquiry depicted in method step 806 indicates thatW_(Ingress)   _((PE1)) _(—) _(for) _(—) _(Egress) _(—) ₁ is greater thanzero, the process proceeds to method step 808 wherein is illustrateddetermination of whether at least one packet is resident at theIngress_(PE1)-Egress_1 queue (e.g., Ingress_(PE1)-Egress_1 queue wouldequate to Ingress_1-Egress_1 queue 516 if PE1 was equal to one,Ingress_2-Egress_1 queue 520 if PE1 was equal to two, etc.). In theevent that a packet is resident at the Ingress_(PE1)-Egress_1 queue, theprocess proceeds to method step 810 wherein is shown that a packet fromthe Ingress_(PE1)-Egress_1 queue is transmitted out of crossbar switch136 via Egress_1 512. Thereafter, the process proceeds to method step812 wherein it is shown that _(WIngress) _(—) _((PE1)) _(—) _(for) _(—)_(Egress) _(—) ₁ is reduced by an amount representative of the packetlength that was transmitted from the Ingress_(PE1)-Egress_1 queue out ofcrossbar switch 136 over Egress_1 512 (the example just described is forvariable length packets; alternatively, if fixed length packets areused, the reduction in the bandwidth counter can be achieved by use of a“shortcut,” which is that the minimum bandwidth is specified by certainnumber of packets to be transmitted during time interval T(Time_Interval_for_Egress_1), and thus the reduction in bandwidth can beaccomplished merely by subtracting the number one from the bandwidthcounter). Thereafter, the process proceeds to method step 813 whichshows that pointer PE1 is updated utilizing an “update point PE1process,” an embodiment of which is described in FIG. 8B2, below.Thereafter, the process proceeds to method step 817 which shows the endof the embodiment of the “packet transmit under the control of minimumbandwidth scheduler” process, as such embodiment is illustrated in FIG.8B1.

In the event that the inquiry depicted in method step 808 yields thedetermination that there is not at least one packet resident at theIngress_(PE1)-Egress_(—) ₁ queue (i.e., the queue is empty), the processproceeds to method step 807, which shows that pointer PE1 is updatedutilizing an “update pointer PE1” process, an embodiment of which isdescribed in FIG. 8B2, below.

In the event that the inquiry of method step 806 indicates thatW_(Ingress) _(—) _((PE1)) _(—) _(for) _(—) _(Egress) _(—) ₁ is zero orless, the process proceeds to method step 807, which shows that pointerPE1 is updated utilizing an “update pointer PE1” process, an embodimentof which is described in FIG. 8B2, below.

Referring now to FIG. 8B2 depicted is a high-level logic flowchartillustrating an embodiment of a process, referenced in method step 813,utilized to update pointer PE1. Method step 813A shows the start of the“update pointer PE1” process. Method step 816 depicts that the value ofpointer PE1 is incremented by one. Thereafter, the process proceeds tomethod step 814 wherein is depicted the inquiry as to whether the valueof pointer PE1 is less than or equal to the highest ordinal number ofingresses associated with Egress_1 512 (e.g., there are threeingresses—Ingress_1 500, Ingress_2 502, and Ingress_3 504—associatedwith Egress_1 512 in FIG. 6). In the event that the value of pointer PE1is less than or equal to the highest ordinal number of ingressesassociated with Egress_1 512, the process proceeds to method step 815wherein it is shown that the “update pointer PE1” process ends and theflow resumes subsequent to the step which called upon the process shownin FIG. 8B2 (e.g., flow will resume subsequent to method step 813 in oneinstance, and subsequent to method step 807 in another instance).

In the event that the inquiry shown in method step 814 yields adetermination that the value of pointer PE1 is greater than the highestordinal number of ingresses, the process proceeds to method step 802which depicts that the value of pointer PE1 is re-initialized to beequal to one. Thereafter, the process proceeds to method step 815wherein it is shown that the “update pointer PE1” process ends.Thereafter, the flow resumes subsequent to the step which called uponthe “update pointer PEB ” process shown in FIG. 8B2 (e.g., flow willresume subsequent to method step 813 in one instance, and subsequent tomethod stop 807 in another instance).

With reference now to FIG. 8C1, depicted is a high-level logic flowchartshowing an embodiment of a process, referenced in method step 811 ofFIG. 8A, whereby a packet is transmitted under the control of excessbandwidth scheduler for Egress_1 600. Method step 811A depicts the startof the “packet transmit under the control of excess bandwidth scheduler”process. Method step 832 depicts the inquiry of whether at least onepacket is resident at Ingress_(PEB1)_Egress_1 queue (e.g.,Ingress_(PEB1)-Egress_1 queue would equate to Ingress_1-Egress_1 queue516 if PEB1 was equal to one, Ingress_2-Egress_1 queue 520 if PEB1 wasequal to two, etc.). In the event that at least one packet is residentat Ingress_(PEB1)_Egress_1 queue, the process proceeds to method step822 and executes from that point. Otherwise, the process proceeds tomethod step 833 which shows that pointer PEB1 is updated utilizing an“update pointer PEB1” process, an embodiment of which is described inFIG. 8C2, below. Thereafter, the process proceeds to method step 832 andexecutes from that point.

Method step 822 shows the transmission of a packet fromIngress_(PEB1)-Egress_1 queue (the notation used indicates thatIngress_(PEB1)-Egress_1 queue equates to Ingress_1-Egress_1 queue 516 ifthe value of PEB1 is equal to one, or equates to Ingress_2-Egress_1queue 520 if the value of PEB1 is equal to two, etc.). Subsequent tomethod step 822, process proceeds to method step 823 which shows thatpointer PEB1 is updated using an “update pointer PEB1” process, anembodiment of which is described in FIG. 8C2, below. Thereafter, theprocess proceeds to method step 825, which shows the end of theembodiment of the “packet transmit under the control of excess bandwidthscheduler” process, as such embodiment is illustrated in FIG. 8C1.

Referring now to FIG. 8C2, depicted is a high-level logic flowchartillustrating an embodiment of a process, referenced in method step 823,utilized to update pointer PEB1. Method step 823A shows the start of“update pointer PEB1” the process. Method step 830 depicts that thevalue of pointer PEB1 is incremented by one. Thereafter, the processproceeds to method step 831 wherein is depicted the inquiry as towhether the value of pointer PEB1 is less than or equal to the highestordinal number of ingresses associated with Egress_1 512 (e.g., thereare three ingresses—Ingress_1 500, Ingress_2 502, and Ingress_3504—associated with Egress_1 512 in FIG. 6). In the event that the valueof pointer PEB1 is less than or equal to the highest ordinal number ofingresses associated with Egress_1 512, the process proceeds to methodstep 835 wherein it is shown that the “update pointer PEB1” processends. Thereafter, the flow resumes subsequent to the step which calledupon the “update pointer PEB1” process shown in FIG. 8C2 (e.g., flowwill resume subsequent to method step 823 in one instance, andsubsequent to method step 833 in another instance).

In the event that the inquiry shown in method step 831 yields adetermination that the value of pointer PEB1 is greater than the highestordinal number of ingresses, the process proceeds to method step 824which depicts that the value of pointer PEB1 is re-initialized to beequal to one. Thereafter, the process proceeds to method step 835wherein it is shown that the “update pointer PEB1” process ends.Thereafter, the flow resumes subsequent to the step which called uponthe process shown in FIG. 8C2 (e.g., flow will resume subsequent tomethod step 813 in one instance, and subsequent to method step 823 inanother instance).

Referring now to FIG. 9, shown is a high-level partially schematic blockdiagram depicting an embodiment of the present invention in the contextof an input queued switch where each ingress-egress pair has a queuewhich can be accessed independently of, and simultaneously with, otherqueues associated with other ingress-egress pairs.

Illustrated is that both switch egress_1 512 and switch egress_2 514have respectively associated with them (1) excess bandwidth schedulers600, 604, and (2) guaranteed minimum bandwidth schedulers 602, 606. Eachguaranteed minimum bandwidth scheduler for each egress assures that eachqueue, and consequently each ingress associated with each queue, isgiven some “guaranteed,” or target, minimum data transmission per unittime (as used herein the term “guaranteed” means essentially a targetwhich will be satisfied if the physical constraints of a switch allow)via the guaranteed minimum bandwidth scheduler's egress, irrespective ofthe priority of the packets that might be resident within each queue.This substantially ensures that no switch ingress is ever completely“starved” of bandwidth, even if the only packets resident within aparticular queue associated with a switch ingress are packets of thelowest possible priority. In the event that no queue requesting datatransmission has an unmet guaranteed minimum data transmission per unittime, the excess bandwidth scheduler for the egress assigns suchbandwidth over and above that bandwidth constituting guaranteed minimumbandwidth to the queues associated with the egress in a fair manner. Itis to be understood that, in at least one embodiment, when utilized witha cross-point buffer switch, the guaranteed minimum bandwidth schedulerand excess bandwidth scheduler at each egress functions substantiallyindependent of guaranteed minimum bandwidth schedulers and excessbandwidth schedulers at resident at other egresses.

Depicted as associated with switch egress_2 514 is guaranteed minimumbandwidth scheduler for egress_2 606 and excess bandwidth scheduler foregress_2 604. As discussed, guaranteed minimum bandwidth scheduler foregress_2 606 is keyed to a guaranteed minimum bandwidth associated witheach switch ingress 500-504. The guaranteed minimum bandwidth isrepresented by a bandwidth counter, associated with each particularswitch ingress 500-504, which is indicative of a relationship between(a) an amount of actual data transmitted, during a prescribed unit oftime T, from each particular switch ingress 500-504 to switch egress_2514 and (b) a target minimum amount of actual data transmission fromeach particular switch ingress 500-504 to switch egress_2 514. Thesebandwidth counters are represented in FIG. 9 as W_(Ingress) _(—) ₁ _(—)_(for) _(—) _(Egress) _(—) ₂ 908, W_(Ingress) _(—) ₂ _(—) _(for) _(—)_(Egress) _(—) ₂ 910, and W_(Ingress) _(—) ₃ _(—) _(for) _(—) _(Egress)_(—) ₂ 912.

With reference now to FIG. 10, depicted is a high-level logic flowchartwhich illustrates the control of the values of bandwidth counters forIngress_1 500, Ingress_2 502, and Ingress_3 504. Method step 1000 showsthe start of the process.

Method step 1002 depicts that Egress_2_Countdown_Timer is initialized toTime_Interval_for_Egress_2. Method step 1004 illustrates thatW_(Ingress) _(—) ₁ _(—) _(for) _(—) _(Egress) _(—) ₂ 908, W_(Ingress)_(—) ₂ _(—) _(for) _(—) _(Egress) _(—) ₂ 910, and W_(Ingress) _(—) ₃_(—) _(for) _(—) _(Egress) _(—) ₂ 912 are each set to values indicativeof the minimum data transmission guaranteed to their respectiveingresses during the Time_Interval_for_Egress_2. Method step 1006illustrates that Egress_2_Countdown_Timer is started and begins tocountdown by some predetermined amount of time decrement (the actualamount of decrement is a design choice). Method step 1008 shows thedetermination of whether Egress_2_Countdown_Timer has counted down to beequal to zero. In the event that Egress_2_Countdown_Timer is greaterthan zero, the process loops to method step 1008. In the event thatEgress_2_Countdown_Timer is less than or equal to zero, the processreturns to method step 1002 and executes from that point. Thus, as canbe seen, the high-level logic flowchart of FIG. 10 ensures thatW_(Ingress) _(—) ₁ _(—) _(for) _(—) _(Egress) _(—) ₂ 908, W_(Ingress)_(—) ₂ _(—) _(for) _(—) _(Egress) _(—) ₂ 910, and W_(Ingress) _(—) ₃_(—) _(for) _(—) _(Egress) _(—) ₂ 912 are each reset to valuesindicative of the minimum bandwidth guaranteed to their respectiveingresses at the start of every successive Time_Interval_for_Egress_2.

It is to be understood that the process illustrated in FIG. 10 is to berunning simultaneously with the process which will now be shown in FIGS.11A, 11B1, 11B2, 11C1, and 11C2. The process illustrated in FIG. 10ensures that W_(Ingress) _(—) ₁ _(—) _(for) _(—) _(Egress) _(—) ₂ 908,W_(Ingress) _(—) ₂ _(—) _(for) _(—) _(Egress) _(—) ₂ 910, andW_(Ingress) _(—) ₃ _(—) _(for) _(—) _(Egress) _(—) ₂ 912 are reset totheir predetermined values after the elapsing of everyTime_Interval_for_Egress_2 period of time. The process shown in FIGS.11A, 11B1, 11B2, 11C1, and 11C2 depicts how W_(Ingress) _(—) ₁ _(—)_(for) _(—) _(Egress) _(—) ₂ 908, W_(Ingress) _(—) ₂ _(—) _(for) _(—)_(Egress) _(—) ₂ 910, and W_(Ingress) _(—) ₃ _(—) _(for) _(—) _(Egress)_(—) ₂ 912 can be utilized to substantially ensure that none ofIngress_1 500, Ingress_2 502, or Ingress_3 504 is being starved ofEgress_2 514 bandwidth.

Referring now to FIG. 11A, shown is a high-level logic flowchartillustrating a process which can be utilized by excess bandwidthscheduler for Egress_2 604 and guaranteed minimum bandwidth schedulerfor Egress_2 606. Method step 1100 shows the start of the process.Method step 1101 depicts that (1) a pointer, “PE2”, used by guaranteedminimum bandwidth scheduler for Egress_2 606 in the manner set forthbelow, is initialized to be equal to one; and (2) a pointer, “PEB2”,used by excess bandwidth scheduler for Egress_2 604 in the manner setforth below, is initialized to be equal to one.

Method step 1103 illustrates the inquiry as to whether at least one ofIngress_1-Egress_2 queue 518, or Ingress_2-Egress_2 queue 522, orIngress_3-Egress_2 queue 526 feeding Egress_2 514 has a packet waitingfor transmission. In the event that the inquiry shown in method step1103 finds that none of Ingress_1-Egress_2 queue 518, orIngress_2-Egress_2 queue 522, or Ingress_3-Egress_2 queue 526 feedingEgress_2 514 has a packet waiting for transmission, the process proceedsto method step 1105 which depicts that no packet is sent. Thereafter,the process proceeds to method step 1103 and executes from that point.

In the event that the inquiry shown in method step 1103 finds that atleast one of Ingress_1-Egress_2 queue 518, or Ingress_2-Egress_2 queue522, or Ingress_3-Egress_2 queue 526 feeding Egress_2 514 has a packetwaiting for transmission, the process proceeds to method step 1107 whichdepicts an embodiment of an inquiry as to whether any one or more queueswhich have a packet waiting for transmission also have a non-zerobandwidth counter; method step 1107 shows that in one embodiment theinquiry is accomplished by checking whether any one of the followingconditions is met:

Is W_(Ingress) _(—) ₁ _(—) _(for) _(—) _(Egress) _(—) ₂ 908 greater thanzero and is at least one packet resident at Ingress_1-Egress_2 queue518? or

Is W_(Ingress) _(—) ₂ _(—) _(for) _(—) _(Egress) _(—) ₂ 910 greater thanzero and is at least one packet resident at Ingress_2-Egress_2 queue522? or

Is W_(Ingress) _(—) ₃ _(—) _(for) _(—) _(Egress) _(—) ₂ 912 greater thanzero and at least one packet is resident at Ingress_3-Egress_2 queue526?

In the event that any one of the foregoing conditions is true, theprocess proceeds to method step 1109 which depicts the transmission of apacket under the control of guaranteed minimum bandwidth scheduler forEgress_2 606 utilizing a process, an embodiment of which is described inFIGS. 11B1 and 11B2, below. In the event that none of the foregoingconditions of method step 1107 is true, the process proceeds to methodstep 1111 which depicts the transmission of a packet under the controlof excess bandwidth scheduler for Egress_2 604, an embodiment of whichis described in FIGS. 11C1 and 11C2, below. Subsequent to theperformance of either method step 1109 or 1111 the process loops back tomethod step 1103 and continues from that point.

With reference now to FIG. 11B1, depicted is a high-level logicflowchart showing an embodiment of a process, referenced in method step1109 of FIG. 11A, whereby a packet is transmitted under the control ofguaranteed minimum bandwidth scheduler for Egress_2 606. Method step1109A depicts the start of the “packet transmit under the control ofminimum bandwidth scheduler” process. Method step 1106 depicts theinquiry of whether W_(Ingress) _(—) _((PE2)) _(—) _(for) _(—) _(Egress)_(—) ₂ (e.g., W_(Ingress) _(—) _((PE2)) _(—) _(for) _(—) _(Egress) _(—)₂ would equate to W_(Ingress) _(—) ₁ _(—) _(for) _(—) _(Egress) _(—) ₂if PE2 was equal to one, W_(Ingress) _(—) ₂ _(—) _(for) _(—) _(Egress)_(—) ₂ if PE2 was equal to two, etc.) is greater than zero.

In the event that the inquiry depicted in method step 1106 indicatesthat W_(Ingress) _(—) _((PE2)) _(—) _(for) _(—) _(Egress) _(—) ₂ isgreater than zero, the process proceeds to method step 1108 wherein isillustrated determination of whether at least one packet is resident atthe Ingress_(PE2)-Egress_2 queue (e.g., Ingress_(PE2)-Egress_2 queuewould equate to Ingress_1-Egress_2 queue 518 if PE2 was equal to one,Ingress_2-Egress_2 queue 522 if PE2 was equal to two, etc.). In theevent that a packet is resident at the Ingress_(PE2)-Egress_2 queue, theprocess proceeds to method step 1110 wherein is shown that a packet fromthe Ingress_(PE2)-Egress_2 queue is transmitted out of crossbar switch136 via Egress_2 514. Thereafter, the process proceeds to method step1112 wherein it is shown that W_(Ingress) _(—) _((PE2)) _(—) _(for) _(—)_(Egress) _(—) ₂ is reduced by an amount representative of the packetlength that was transmitted from the Ingress_(PE2)-Egress_2 queue out ofcrossbar switch 136 over Egress_2 514 (the example just described is forvariable length packets; alternatively, if fixed length packets areused, the reduction in the bandwidth counter can be achieved by use of a“shortcut,” which is that the minimum bandwidth is specified by certainnumber of packets to be transmitted during time interval T(Time_Interval_for_Egress_2), and thus the reduction in bandwidth can beaccomplished merely by subtracting the number one from the bandwidthcounter). Thereafter, the process proceeds to method step 1113 whichshows that pointer PE2 is updated utilizing an “update point PE2process,” an embodiment of which is described in FIG. 11B2, below.Thereafter, the process proceeds to method step 1117 which shows the endof the embodiment of the “packet transmit under the control of minimumbandwidth scheduler” process, as such embodiment is illustrated in FIG.11B1.

In the event that the inquiry depicted in method step 1108 yields thedetermination that there is not at least one packet resident at theIngress_(PE2)-Egress_2 queue (i.e., the queue is empty), the processproceeds to method step 1107, which shows that pointer PE2 is updatedutilizing an “update pointer PE2” process, an embodiment of which isdescribed in FIG. 11B2, below.

In the event that the inquiry of method step 1106 indicates thatW_(Ingress) _(—) _((PE2)) _(—) _(for) _(—) _(Egress) _(—) ₂ is zero orless, the process proceeds to method step 1107, which shows that pointerPE2 is updated utilizing an “update pointer PE2” process, an embodimentof which is described in FIG. 11B2, below.

Referring now to FIG. 11B2 depicted is a high-level logic flowchartillustrating an embodiment of a process, referenced in method step 1113,utilized to update pointer PE2. Method step 1113A shows the start of the“update pointer PE2” process. Method step 1116 depicts that the value ofpointer PE2 is incremented by one. Thereafter, the process proceeds tomethod step 1114 wherein is depicted the inquiry as to whether the valueof pointer PE2 is less than or equal to the highest ordinal number ofingresses associated with Egress_2 514 (e.g., there are threeingresses—Ingress_1 500, Ingress_2 502, and Ingress_3 504—associatedwith Egress_2 514 in FIG. 9). In the event that the value of pointer PE2is less than or equal to the highest ordinal number of ingressesassociated with Egress_2 514, the process proceeds to method step 1115wherein it is shown that the “update pointer PE2” process ends and theflow resumes subsequent to the step which called upon the process shownin FIG. 11B2 (e.g., flow will resume subsequent to method step 1113 inone instance, and subsequent to method step 1107 in another instance).

In the event that the inquiry shown in method step 1114 yields adetermination that the value of pointer PE2 is greater than the highestordinal number of ingresses, the process proceeds to method step 1102which depicts that the value of pointer PE2 is re-initialized to beequal to one. Thereafter, the process proceeds to method step 1115wherein it is shown that the “update pointer PE2” process ends.Thereafter, the flow resumes subsequent to the step which called uponthe “update pointer PE2” process shown in FIG. 11B2 (e.g., flow willresume subsequent to method step 1113 in one instance, and subsequent tomethod stop 1107 in another instance).

With reference now to FIG. 11C1, depicted is a high-level logicflowchart showing an embodiment of a process, referenced in method step1111 of FIG. 11A, whereby a packet is transmitted under the control ofexcess bandwidth scheduler for Egress_2 604. Method step 1111A depictsthe start of the “packet transmit under the control of excess bandwidthscheduler” process. Method step 1132 depicts the inquiry of whether atleast one packet is resident at Ingress_(PEB2)_Egress_2 queue (e.g.,Ingress_(PEB2)-Egress_2 queue would equate to Ingress_1-Egress_2 queue518 if PEB2 was equal to one, Ingress_2-Egress_2 queue 522 if PEB2 wasequal to two, etc.). In the event that at least one packet is residentat Ingress_(PEB2)_Egress_2 queue, the process proceeds to method step1122 and executes from that point. Otherwise, the process proceeds tomethod step 1133 which shows that pointer PEB2 is updated utilizing an“update pointer PEB2” process, an embodiment of which is described inFIG. 11C2, below. Thereafter, the process proceeds to method step 1132and executes from that point.

Method step 1122 shows the transmission of a packet fromIngress_(PEB2)-Egress_2 queue (the notation used indicates thatIngress_(PEB2)-Egress_2 queue equates to Ingress_1-Egress_2 queue 518 ifthe value of PEB2 is equal to one, or equates to Ingress_2-Egress_2queue 522 if the value of PEB2 is equal to two, etc.). Subsequent to themethod step 1122, process proceeds to method step 1123 which shows thatpointer PEB2 is updated using an “update pointer PEB2” process, anembodiment of which is described in FIG. 11C2, below. Thereafter, theprocess proceeds to method step 1125, which shows the end of theembodiment of the “packet transmit under the control of excess bandwidthscheduler” process, as such embodiment is illustrated in FIG. 11C1.

Referring now to FIG. 11C2, depicted is a high-level logic flowchartillustrating an embodiment of a process, referenced in method step 1123,utilized to update pointer PEB2. Method step 1123A shows the start of“update pointer PEB2” the process. Method step 1130 depicts that thevalue of pointer PEB2 is incremented by one. Thereafter, the processproceeds to method step 1131 wherein is depicted the inquiry as towhether the value of pointer PEB2 is less than or equal to the highestordinal number of ingresses associated with Egress_2 514 (e.g., thereare three ingresses—Ingress_1 500, Ingress_2 502, and Ingress_3504—associated with Egress_2 514 in FIG. 9). In the event that the valueof pointer PEB2 is less than or equal to the highest ordinal number ofingresses associated with Egress_2 514, the process proceeds to methodstep 1135 wherein it is shown that the “update pointer PEB2” processends. Thereafter, the flow resumes subsequent to the step which calledupon the “update pointer PEB2” process shown in FIG. 11C2 (e.g., flowwill resume subsequent to method step 1123 in one instance, andsubsequent to method step 1133 in another instance).

In the event that the inquiry shown in method step 1131 yields adetermination that the value of pointer PEB2 is greater than the highestordinal number of ingresses, the process proceeds to method step 1124which depicts that the value of pointer PEB2 is re-initialized to beequal to one. Thereafter, the process proceeds to method step 1135wherein it is shown that the “update pointer PEB2” process ends.Thereafter, the flow resumes subsequent to the step which called uponthe process shown in FIG. 11C2 (e.g., flow will resume subsequent tomethod step 1113 in one instance, and subsequent to method step 1123 inanother instance).

The foregoing has set forth specific examples of embodiments of theinvention in the context of a 3×2 crosspoint switch (i.e., three ingresstwo egress switch). The first example showed the functioning of anembodiment with respect Egress_1 512. The second example showed thefunctioning of an embodiment with respect Egress_2 514. Those skilled inthe art will recognize that the principles shown in the specific examplecan be generalized to any M×N crosspoint switch.

Referring now to FIG. 12, shown is a high-level partially schematicblock diagram depicting an embodiment of the present invention in thecontext of an input queued switch where each ingress-egress pair has aqueue which can be accessed independently of, and simultaneously with,other queues associated with other ingress-egress pairs. Examples ofqueues are illustrated in FIG. 12 as ingress-egress queues 1216-1226,each of which is shown respectively connected between its associatedparticular ingress-egress pair.

Illustrated is that both switch egress_1 1212 and switch egress_N 1214have respectively associated with them (1) excess bandwidth schedulers1200, 1204, and (2) guaranteed minimum bandwidth schedulers 1202, 1206.Each guaranteed minimum bandwidth scheduler for each egress assures thateach queue, and consequently each ingress associated with each queue, isgiven some “guaranteed,” or target, minimum data transmission per unittime (as used herein the term “guaranteed” means essentially a targetwhich will be satisfied if the physical constraints of a switch allow)via the guaranteed minimum bandwidth scheduler's egress, irrespective ofthe priority of the packets that might be resident within each queue.This substantially ensures that no switch ingress is ever completely“starved” of bandwidth, even if the only packets resident within aparticular queue associated with a switch ingress are packets of thelowest possible priority. In the event that no queue requesting datatransmission has an unmet guaranteed minimum data transmission per unittime, the excess bandwidth scheduler for the egress assigns suchbandwidth over and above that bandwidth constituting guaranteed minimumbandwidth to the queues associated with the egress in a fair manner. Itis to be understood that, in at least one embodiment, when utilized witha cross-point buffer switch, the guaranteed minimum bandwidth schedulerand excess bandwidth scheduler at each egress functions substantiallyindependent of guaranteed minimum bandwidth schedulers and excessbandwidth schedulers at resident at other egresses.

Depicted as associated with switch egress_N 1214 is guaranteed minimumbandwidth scheduler for egress_N 1206 and excess bandwidth scheduler foregress_N 1204. As discussed, guaranteed minimum bandwidth scheduler foregress_N 1206 is keyed to a guaranteed minimum bandwidth associated witheach switch ingress 1201, 1203, 1205. The guaranteed minimum bandwidthis represented by a bandwidth counter, associated with each particularswitch ingress 1201, 1203, 1205, which is indicative of a relationshipbetween (a) an amount of actual data transmitted, during a prescribedunit of time T, from each particular switch ingress 1201, 1203, 1205 toswitch egress_N 1214 and (b) a target minimum amount of actual datatransmission from each particular switch ingress 1201, 1203, 1205 toswitch egress_N 1214. These bandwidth counters are represented in FIG.12 as W_(Ingress) _(—) ₁ _(—) _(for) _(—) _(Egress) _(—) _(N) 1228,W_(Ingress) _(—) ₂ _(—) _(for) _(—) _(Egress) _(—) _(N) 1230, andW_(Ingress) _(—) _(M) _(—) _(for) _(—) _(Egress) _(—) _(N) 1232.

With reference now to FIG. 13, depicted is a high-level logic flowchartwhich illustrates the control of the values of bandwidth counters forIngress_1 1201, Ingress_2 1203, and Ingress_M 1205. Method step 1300shows the start of the process. Method step 1302 depicts thatEgress_N_Countdown_Timer is initialized to Time_Interval for_Egress_N.Method step 1304 illustrates that W_(Ingress) _(—) ₁ _(—) _(for) _(—)_(Egress) _(—) _(N) 1228, W_(Ingress) _(—) ₂ ₁₃ _(for) _(—) _(Egress)_(—) _(N) 1230, and W_(Ingress) _(—) _(M) _(—) _(for) _(—) _(Egress)_(—) _(N) 1232 are each set to values indicative of the minimum datatransmission guaranteed to their respective ingresses during theTime_Interval_for_Egress_N. Method step 1306 illustrates thatEgress_N_Countdown_Timer is started and begins to countdown by somepredetermined amount of time decrement (the actual amount of decrementis a design choice). Method step 1308 shows the determination of whetherEgress_N_Countdown_Timer has counted down to be equal to zero. In theevent that Egress_N_Countdown_Timer is greater than zero, the processloops to method step 1308. In the event that Egress_N_Countdown_Timer isless than or equal to zero, the process returns to method step 1302 andexecutes from that point. Thus, as can be seen, the high-level logicflowchart of FIG. 13 ensures that W_(Ingress) _(—) ₁ _(—) _(for) _(—)_(Egress) _(—) _(N) 1228, W_(Ingress) _(—) ₂ _(—) _(for) _(—) _(Egress)_(—) _(N) 1230, and W_(Ingress) _(—) _(M) _(—) _(for) _(—) _(Egress)_(—) _(N) 1232 are each reset to values indicative of the minimumbandwidth guaranteed to their respective ingresses at the start of everysuccessive Time_Interval_for_Egress_N.

It is to be understood that the process illustrated in FIG. 13 is to berunning simultaneous with the process which will now be shown in FIGS.14A, 14B1, 14B2, 14C1, and 14C2. The process illustrated in FIG. 13ensures that W_(Ingress) _(—) ₁ _(—) _(for) _(—) _(Egress) _(—) _(N)1228, W_(Ingress) _(—) ₂ _(—) _(for) _(—) _(Egress) _(—) _(N) 1230, andW_(Ingress) _(—) _(M) _(—) _(for) _(—) _(Egress) _(—) _(N) 1232 arereset to their predetermined values after the elapsing of everyTime_Interval_for_Egress_N period of time. The process shown in FIGS.14A, 14B1, 14B2, 14C1, and 14C2 depicts how W_(Ingress) _(—) ₁ _(—)_(for) _(—) _(Egress) _(—) _(N) 1228, W_(Ingress) _(—) ₂ _(—) _(for)_(—) _(Egress) _(—) _(N) 1230, and W_(Ingress) _(—) _(M) _(—) _(for)_(—) _(Egress) _(—) _(N) 1232 can be utilized to substantially ensurethat none of Ingress_1 1201, Ingress_2 1203, or Ingress_M 1205 is beingstarved of Egress_N 1214 bandwidth.

Referring now to FIG. 14A, shown is a high-level logic flowchartillustrating a process which can be utilized by excess bandwidthscheduler for Egress_N 1204 and guaranteed minimum bandwidth schedulerfor Egress_N 1206. Method step 1400 shows the start of the process.Method step 1401 depicts that (1) a pointer, “PE_N”, used by guaranteedminimum bandwidth scheduler for Egress_N 1202 in the manner set forthbelow, is initialized to be equal to one; and (2) a pointer, “PEB_N”,used by excess bandwidth scheduler for Egress_N 1204 in the manner setforth below, is initialized to be equal to one.

Method step 1403 illustrates the inquiry as to whether at least one ofIngress_-Egress_N queue 1218, or Ingress_2-Egress_N queue 1222, orIngress_M_Egress_N queue 1226 feeding Egress_N 1214 has a packet waitingfor transmission. In the event that the inquiry shown in method step1403 finds that none of Ingress_1_Egress_N queue 1218, orIngress_2-Egress_N queue 1222, or Ingress_M-Egress_N queue 1226 feedingEgress_N 1214 has a packet waiting for transmission, the processproceeds to method step 1405 which depicts that no packet is sent.Thereafter, the process proceeds to method step 1403 and executes fromthat point.

In the event that the inquiry shown in method step 1403 finds that atleast one of Ingress_1-Egress_N queue 1218, or Ingress_2-Egress_N queue1222, or Ingress_M-Egress_N queue 1226 feeding Egress_(')N 1214 has apacket waiting for transmission, the process proceeds to method step1407 which depicts an embodiment of an inquiry as to whether any one ormore queues which have a packet waiting for transmission also have anon-zero bandwidth counter; that is, method step 1407 shows that in oneembodiment the inquiry is accomplished by checking whether any one ofthe following conditions is met:

Is W_(Ingress) _(—) ₁ _(—) _(for) _(—) _(Egress) _(—) _(N) 1228 greaterthan zero and is at least one packet resident at Ingress_1-Egress_Nqueue 1218? or

Is W_(Ingress) _(—) ₂ _(—) _(for) _(—) _(Egress) _(—) _(N) 1230 greaterthan zero and is at least one packet resident at Ingress_2-Egress_Nqueue 1222? or

Is W_(Ingress) _(—) _(M) _(—) _(for) _(—) _(Egress) _(—) _(N) 1232greater than zero and at least one packet is resident at Ingress₁₃M-Egress_N queue 1228?

In the event that any one of the foregoing conditions is true, theprocess proceeds to method step 1409 which depicts the transmission of apacket under the control of guaranteed minimum bandwidth scheduler forEgress_N 1206 utilizing a process, an embodiment of which is describedin FIGS. 14B1 and 14B2, below. In the event that none of the foregoingconditions of method step 1407 is true, the process proceeds to methodstep 1411 which depicts the transmission of a packet under the controlof excess bandwidth scheduler for Egress_N 1204, an embodiment of whichis described in FIGS. 14C1 and 14C2, below. Subsequent to theperformance of either method step 1409 or 1411 the process loops back tomethod step 1403 and continues from that point.

With reference now to FIG. 14B1, depicted is a high-level logicflowchart showing an embodiment of a process, referenced in method step1409 of FIG. 14A, whereby a packet is transmitted under the control ofguaranteed minimum bandwidth scheduler for Egress_N 1206. Method step1409A depicts the start of the “packet transmit under the control ofminimum bandwidth scheduler” process. Method step 1406 depicts theinquiry of whether W_(Ingress) _(—) _((PE) _(—) _(N)) _(—) _(for) _(—)_(Egress) _(—) _(N) (e g., W_(Ingress) _(—) _((PE) _(—) _(N)) _(—)_(for) _(—) _(Egress) _(—) _(N) would equate to W_(Ingress) _(—) ₁ _(—)_(for) _(—) _(Egress) _(—) _(N) if PE_N was equal to one, W_(Ingress)_(—) ₂ _(—) _(for) _(—) _(Egress) _(—) _(N) if PE_N was equal to two,etc.) is greater than zero.

In the event that the inquiry depicted in method step 1406 indicatesthat W_(Ingress) _(—) _((PE) _(—) _(N)) _(—) _(for) _(—) _(Egress) _(—)_(N) is greater than zero, the process proceeds to method step 1408wherein is illustrated determination of whether at least one packet isresident at the Ingress_(PE_N)-Egress_N queue (e.g.,Ingress_(PE_N)-Egress_N queue would equate to Ingress_1 -Egress_N queue1218 if PE_N was equal to one, Ingress_2-Egress_N queue 1222 if PE_N wasequal to two, etc.). In the event that a packet is resident at theIngress_(PE_N)-Egress_N queue, the process proceeds to method step 1410wherein is shown that a packet from the Ingress_(PE_N)-Egress_N queue istransmitted out of crossbar switch 136 via Egress_N 1214. Thereafter,the process proceeds to method step 1412 wherein it is shown thatW_(Ingress) _(—) _((PE) _(—) _(N)) _(—) _(for) _(—) _(Egress) _(—) _(N)is reduced by an amount representative of the packet length that wastransmitted from the Ingress_(PE_N)-Egress_N queue out of crossbarswitch 136 over Egress_N 1214 (the example just described is forvariable length packets; alternatively, if fixed length packets areused, the reduction in the bandwidth counter can be achieved by use of a“shortcut,” which is that the minimum bandwidth is specified by certainnumber of packets to be transmitted during time interval T, and thus thereduction in bandwidth can be accomplished merely by subtracting thenumber one from the bandwidth counter). Thereafter, the process proceedsto method step 1413 which shows that pointer PE_N is updated utilizingan “update point PE_N process,” an embodiment of which is described inFIG. 14B2, below. Thereafter, the process proceeds to method step 1417which shows the end of the embodiment of the “packet transmit under thecontrol of minimum bandwidth scheduler” process, as such embodiment isillustrated in FIG. 14B1.

In the event that the inquiry depicted in method step 1408 yields thedetermination that there is not at least one packet resident at theIngress_(PE_N)-Egress_N queue (i.e., the queue is empty), the processproceeds to method step 1407, which shows that pointer PE_N is updatedutilizing an “update pointer PE_N” process, an embodiment of which isdescribed in FIG. 14B2, below.

In the event that the inquiry of method step 1406 indicates thatW_(Ingress) _(—) (PE _(—) _(N)) _(—) _(for) _(—) _(Egress) _(—) _(N) iszero or less, the process proceeds to method step 1407, which shows thatpointer PE_N is updated utilizing an “update pointer PE_N” process, anembodiment of which is described in FIG. 14B2, below.

Referring now to FIG. 14B2 depicted is a high-level logic flowchartillustrating an embodiment of a process, referenced in method step 1413,utilized to update pointer PE_N. Method step 1413A shows the start ofthe “update pointer PE_N” process. Method step 1416 depicts that thevalue of pointer PE_N is incremented by one. Thereafter, the processproceeds to method step 1414 wherein is depicted the inquiry as towhether the value of pointer PE_N is less than or equal to the highestordinal number of ingresses associated with Egress_N 1214 (e.g., thereare three ingresses—Ingress_1 1201, Ingress_2 1203, and Ingress_M1205—associated with Egress_N 1214 in FIG. 12). In the event that thevalue of pointer PE_N is less than or equal to the highest ordinalnumber of ingresses associated with Egress_N 1214, the process proceedsto method step 1415 wherein it is shown that the “update pointer PE_N”process ends and the flow resumes subsequent to the step which calledupon the process shown in FIG. 14B2 (e.g., flow will resume subsequentto method step 1413 in one instance, and subsequent to method step 1407in another instance).

In the event that the inquiry shown in method step 1414 yields adetermination that the value of pointer PE_N is greater than the highestordinal number of ingresses, the process proceeds to method step 1402which depicts that the value of pointer PE_N is re-initialized to beequal to one. Thereafter, the process proceeds to method step 1415wherein it is shown that the “update pointer PE_N” process ends.Thereafter, the flow resumes subsequent to the step which called uponthe “update pointer PE_N” process shown in FIG. 14B2 (e.g., flow willresume subsequent to method step 1413 in one instance, and subsequent tomethod stop 1407 in another instance).

With reference now to FIG. 14C1, depicted is a high-level logicflowchart showing an embodiment of a process, referenced in method step1411 of FIG. 14A, whereby a packet is transmitted under the control ofexcess bandwidth scheduler for Egress_N 1204. Method step 1411A depictsthe start of the “packet transmit under the control of excess bandwidthscheduler” process. Method step 1432 depicts the inquiry of whether atleast one packet is resident at Ingress_(PEB_N)_Egress_N queue (e.g.,Ingress_(PEB_N)-Egress_N queue would equate to Ingress_-Egress_N queue1218 if PEB_N was equal to one, Ingress_2-Egress_N queue 1222 if PEB_Nwas equal to two, etc.). In the event that at least one packet isresident at Ingress_(PEB_N)_Egress_N queue, the process proceeds tomethod step 1422 and executes from that point. Otherwise, the processproceeds to method step 1433 which shows that pointer PEB_N is updatedutilizing an “update pointer PEB_N” process, an embodiment of which isdescribed in FIG. 14C2, below. Thereafter, the process proceeds tomethod step 1432 and executes from that point.

Method step 1422 shows the transmission of a packet fromIngress_(PEB_N)-Egress_N queue (the notation used indicates thatIngress_(PEB_N)-Egress_N queue equates to Ingress_1-Egress_N queue 1218if the value of PEB_N is equal to one, or equates to Ingress_2-Egress_Nqueue 1222 if the value of PEB_N is equal to two, etc.). Subsequent tomethod step 1422, process proceeds to method step 1423 which shows thatpointer PEB_N is updated using an “update pointer PEB_N” process, anembodiment of which is described in FIG. 14C2, below. Thereafter, theprocess proceeds to method step 1425, which shows the end of theembodiment of the “packet transmit under the control of excess bandwidthscheduler” process, as such embodiment is illustrated in FIG. 14C1.

Referring now to FIG. 14C2, depicted is a high-level logic flowchartillustrating an embodiment of a process, referenced in method step 1423,utilized to update pointer PEB_N. Method step 1423A shows the start of“update pointer PEB_N” the process. Method step 1430 depicts that thevalue of pointer PEB_N is incremented by one. Thereafter, the processproceeds to method step 1431 wherein is depicted the inquiry as towhether the value of pointer PEB_N is less than or equal to the highestordinal number of ingresses associated with Egress_N 1214 (e.g., thereare three ingresses—Ingress_1 1201, Ingress_2 1203, and Ingress_M1205—associated with Egress_N 1214 in FIG. 12). In the event that thevalue of pointer PEB_N is less than or equal to the highest ordinalnumber of ingresses associated with Egress_N 1214, the process proceedsto method step 1435 wherein it is shown that the “update pointer PEB_N”process ends. Thereafter, the flow resumes subsequent to the step whichcalled upon the “update pointer PEB_N” process shown in FIG. 14C2 (e.g.,flow will resume subsequent to method step 1423 in one instance, andsubsequent to method step 1433 in another instance).

In the event that the inquiry shown in method step 1431 yields adetermination that the value of pointer PEB_N is greater than thehighest ordinal number of ingresses, the process proceeds to method step1424 which depicts that the value of pointer PEB_N is re-initialized tobe equal to one. Thereafter, the process proceeds to method step 1435wherein it is shown that the “update pointer PEB_N” process ends.Thereafter, the flow resumes subsequent to the step which called uponthe process shown in FIG. 14C2 (e.g., flow will resume subsequent tomethod step 1413 in one instance, and subsequent to method step 1423 inanother instance).

II. Crossbar Switch Having Input Buffers

The foregoing discussion examined the application of the “minimumbandwidth guarantee for crossbar switches having input queues” scheme inthe context of a cross-point buffer switch. The following discussionexamines application of the “minimum bandwidth guarantee for crossbarswitches having input queues” scheme in the context of a crossbar switchhaving queues wherein each queue at a particular ingress is notaccessible independently of other queues at that particular ingress.

With reference now to FIGS. 15 and 16, shown are a pictographicrepresentations of the “minimum bandwidth guarantee for crossbarswitches having input queues” scheme employed within a crossbar switchhaving non-independently accessible input buffers (hereinafter, for sakeof brevity, a crossbar switch having non-independently accessible inputbuffers will be referred to as an “input-buffered crossbar switch”). Ascan be seen, the crossbar switch is similar to the cross-point bufferswitch shown in FIG. 6, except that “queues” 1516-1526 are shown ascontiguous areas of input buffers and that the schedulers must accessthe “queues” 1516-1526 through memory controllers 1540-1544.

As shown, bandwidth counters are still associated with ingress-egresspairs in substantially the same fashion as was described in relation toFIG. 6. However, the fact that only one “queue” at an ingress can beaccessed at a particular time significantly complicates the way in whichbandwidth counters can be utilized by the devices shown in FIGS. 15 and16 to apply the “minimum bandwidth guarantee for crossbar switcheshaving input queues” to input-buffered crossbar switches. That is, whenan attempt is made to directly employ the “minimum bandwidth guaranteefor crossbar switches having input queues” scheme in an input-bufferedcrossbar switch, several problems arise which must be overcome to allowsubstantially the optimum functioning of the scheme.

As discussed above, because each egress queue at each ingress in across-point buffer switch is independently accessible, the egressschedulers at each egress run autonomously (in relation to other egressschedulers), because, in a cross-point buffer switch, an egressconnected to a queue at an ingress does not prevent a different egressfrom connecting with another queue at the same ingress. As has beendemonstrated, the foregoing is not true for an input-buffered crossbarswitch. Each “queue” at an input-buffered crossbar switch ingress (e.g.,Ingess_1 -Egress_1 queue 1516 and Ingress_2-Egress _1 queue 1518) isactually a region of memory to which access is controlled by a memorycontroller (e.g., single access memory controller 1540). Consequently,only one “queue” (e.g., Ingess_1-Egress_1 queue 1516, orIngress_2-Egress_1 queue 1518) at each input-buffered crossbar switchingress (e.g., switch ingress_1 1511) can connect with any oneinput-buffered crossbar switch egress (Egress_1 1512) at any particulartime.

Thus, at any one input-buffered crossbar switch ingress at which two ormore queues are vying, or contending, for access to one or moreinput-buffered crossbar switch egresses, the contention between the twoor more vying queues must be resolved so that a proper connection can beestablished for the input-buffered crossbar switch ingress, because aconnection between one queue at a particular input-buffered crossbarswitch ingress and a input-buffered crossbar switch egress forestallsany other connection to any other queue at that input-buffered crossbarswitch ingress.

One way to solve the foregoing noted problem is to allow the queues ateach input-buffered crossbar switch ingress to resolve their contentionsamongst themselves. Unfortunately, this way is sub-optimum because oneor more queues at another input-buffered crossbar switch ingress mightbe vying for access to the same input-buffered crossbar switch egress.Since queues at each input-buffered crossbar switch ingress do not “talkto each other,” it was found that having the ingresses resolve their owninternal contentions was sub-optimum in that even though contentions areresolved internal to, say, two different input-buffered crossbar switchingresses, those two different input-buffered crossbar switch ingressesmight still schedule themselves to connect with the same input-bufferedcrossbar switch egress, which would mean one of the ingresses would haveto wait for connection.

The solution, described in detail below, is to move the contentionresolution decisions from the input-buffered crossbar switch ingressesto each input-buffered crossbar switch egress. Thus, each input-bufferedcrossbar switch egress can examine all input-buffered crossbar switchingresses that are needing to connect with it, and resolve anyinput-buffered crossbar switch ingress contentions so that only one ofseveral input-buffered crossbar switch ingresses feeding a particularinput-buffered crossbar switch egress will be scheduled to connect withthe particular input-buffered crossbar switch egress. This solution isillustrated pictographically in FIGS. 15 and 16 by Egress_1 Scheduler1562, which utilizes guaranteed minimum bandwidth and excess bandwidthconstraints to resolve any contentions arising from more than one queueat the same ingress vying for access to an egress, and builds CandidateIngress Queue-Egress Physical Connections Column Matrix forEgress_1—which is viewed below, for sake of illustration, as a column ofa Candidate Ingress Queue-Egress Physical Connections Matrix, andEgress_2 Scheduler 1566, which utilizes guaranteed minimum bandwidth andexcess bandwidth constraints to resolve any contentions arising frommore than one queue at the same ingress vying for access to an egress,and builds candidate Ingress Queue-Egress Physical Connections ColumnMatrix for Egress_2—which is viewed below, for sake of illustration, asa column of a Candidate Ingress Queue-Egress Physical ConnectionsMatrix.

The noted solution to the first sub-problem is a conceptual shift wherethe problem of contention resolution at each ingress is moved to andviewed from to the global viewpoint of each egress. This eliminates thefirst sub-problem, but gives rise to a second sub-problem, which arisesfrom the fact that each egress needs to be aware of the fact that aconnection between a fellow egress and a particular ingress forestallsany other egress from connecting with the so-connected ingress. That is,since the solution for the first problem allows each egress to scheduleconnections for itself independent of other egresses, the possibilityarises that two egresses may schedule connections for themselves to thesame ingress.

The solution to the second sub-problem is to systematically examine eachegress scheduler's scheduled candidate connections, and eliminatescheduling conflicts between two or more egresses scheduled to accessthe same ingress. Thereafter, data is transmitted and bandwidth countersare adjusted as is appropriate. This solution is illustratedpictographically in FIGS. 15 and 16 by Egress_1's Ingress Queue-EgressConnection Scheduler 1564 which utilizes the Candidate IngressQueue-Egress Physical Connections Matrix, resolves any contentionsarising from more than one egress scheduled to connect to the sameingress, and builds Granted Ingress Queue-Egress Physical ConnectionsRow Matrix for Egress_1—which is viewed below, for sake of illustration,as a row of a Granted Ingress Queue-Egress Physical Connections Matrix,and Egress_2's Ingress Queue-Egress Connection Scheduler 1568 whichutilizes the Candidate Ingress Queue-Egress Physical Connections Matrix,resolves any contentions arising from more than one egress scheduled toconnect to the same ingress, and builds Granted Ingress Queue-EgressPhysical Connections Row Matrix for Egress_2—which is viewed below, forsake of illustration, as a row of a Granted Ingress Queue-EgressPhysical Connections Matrix.

Transmission unit for Egress_1 1501 utilizes Granted IngressQueue-Egress Physical Connections Matrix for Egress_1—which is viewedbelow, for sake of illustration, as a row of a Granted IngressQueue-Egress Physical Connections Matrix—to establish an appropriateEgress_1 1512 connection with a particular ingress and, if appropriate,subsequent to data transmission decreases the bandwidth counterassociated with the queue from which the data was transmitted (e.g., ifthe queue from which data was transmitted had a non-zero bandwidthcounter, the bandwidth counter is decremented; otherwise, the bandwidthcounter is left undisturbed). Transmission unit for Egress_2 1502utilizes Granted Ingress Queue-Egress Physical Connections Matrix forEgress_2—which is viewed below, for sake of illustration, as a row of aGranted Ingress Queue-Egress Physical Connections Matrix—to establish anappropriate Egress_2 1514 connection with a particular Ingress and, ifappropriate, subsequent to data transmission decreases the bandwidthcounter associated with the queue from which the data was transmitted(e.g., if the queue from which data was transmitted had a non-zerobandwidth counter, the bandwidth counter is decremented; otherwise, thebandwidth counter is left undisturbed).

As has been mentioned, various column and row vectors, or matrices(e.g., Candidate Ingress Queue-Egress Physical Connections Column Matrixfor Egress_1; Granted Ingress Queue-Egress Physical Connections RowMatrix for Egress_1) will be viewed, or treated, in the discussion belowas columns or rows of other matrices (e.g., as a column of a CandidateIngress Queue-Egress Physical Connections Matrix, or as a row of aGranted Ingress Queue-Egress Physical Connections Matrix). The reasonfor this is that the overall operation of the application of the“minimum bandwidth guarantee for crossbar switches having input queues”scheme to input-buffered crossbar switches is easier to understand ifthe scheme is described as a sequential fashion, with operations to beperformed in parallel at each egress being described via the descriptionof such operations as being executed at each egress in sequence.However, it should be noted that although the application will bedescribed in a sequential fashion, in one embodiment the operationsdescribed as executing in sequence at each egress are actuallyimplemented via such processes operating in parallel at each egress withthe coordinating effects arising from the sequential processes,described below, being achieved by communications between the processesexecuting at the respective egresses. Such a transition from sequentialto parallel operation is well within the ambit of one of ordinary skillin the art, and requires only minimal experimentation.

In order to understand the operation of processes and devices describedbelow, it is necessary to introduce some new concepts and terminology.FIGS. 17 and 18 introduce these new concepts and terminology via the useof a first example (shown in FIG. 17) which explains the concepts andterminology in the context of a crosspoint buffer switch environment(with such example constituting yet another embodiment of the presentinvention being practiced in a cross-point buffer switch environment),and a second example which modifies the concepts and terminologyintroduced in FIG. 17 in a manner appropriate to input-buffered crossbarswitch environment.

Referring now to FIG. 17, shown is an example of cross-point bufferswitch 1700 responding to a particular state of events illustrated inpending packets requesting transmission diagram 1702. (Cross-pointbuffer switch 1700 is depicted in a slightly different format than thatpreviously used to depict a cross-point buffer switch). Cross-pointbuffer switch 1700 is depicted as a 4×4 switch, having four ingresses1704 and four egresses 1706, with each ingress-egress pair havingassociated with it a queue, denoted in FIG. 17 asQ_(first subscript, second subscript) where “first subscript” equates tothe queue's ingress number and where “second subscript” equates to thequeue's egress number.

Shown in pending packets requesting transmission diagram 1702 is thatthere are two packets at ingress #1 requesting transmission. Depicted isthat a first packet at ingress #1 is requesting transmission from theswitch via egress #2, and that a second packet at ingress #1 isrequesting transmission from the switch via egress #3. Illustrated isthat there are two packets at ingress #2 requesting transmission. Shownis that a first packet at ingress #2 is requesting transmission from theswitch via egress #2 and that a second packet at ingress #2 isrequesting transmission from the switch via egress #4. Depicted is thatthere is one packet at ingress #3 requesting transmission from theswitch via egress #1. Illustrated is that there is one packet at ingress#4 requesting transmission from the switch via egress #4.

Shown in Pending Request Pattern Matrix 1708 is that the fact that thereare one or more pending packets requesting transmission, as illustratedin pending packets requesting transmission diagram 1702, can beillustrated in matrix form. In Pending Request Pattern Matrix 1708 therows of the matrix represent ingress #1 through #4, while the columns ofthe matrix represent egress #1 through egress #4. The presence of a “1”within a particular row and column of Pending Request Pattern Matrix1708 indicates that at least one packet is pending transmission (i.e. isqueued) from the ingress to the egress denoted by the matrix entry. Thepresence of a “0” within a particular row and column of pending requestmatrix 1708 indicates that no packet is pending transmission (i.e. isqueued) from the ingress to the egress denoted by the matrix entry.Consequently, shown in Pending Request Pattern Matrix 1708 is thatcolumn 4 has an entry of “1” in row #2—corresponding to the fact that atleast one pending packet requesting transmission via egress #4 is queuedat ingress #2, an entry of “1” in row #4—corresponding to the fact thatat least one pending packet requesting transmission via egress #4 isqueued at ingress #2, an entry of “0” in row #1—corresponding to thefact that no pending packets requesting transmission via egress #4 arequeued at ingress #1, and an entry of “0” in row #3—corresponding to thefact that no pending packets requesting transmission via egress #4 arequeued at ingress #3.

Likewise, illustrated in Pending Request Pattern Matrix 1708 is thatcolumn 3 has an entry of “1” in row #1—corresponding to the fact that itleast one pending packet requesting transmission via egress #3 is queuedat ingress #1, and has entries of “0” in the remaining rows (e.g., row#2, #3, and #4) of column 3—corresponding to the fact that no pendingpackets requesting transmission via egress #3 are queued at eitheringress #2, #3, or #4. Further shown in Pending Request Pattern Matrix1708 is that column 2 has an entry of “1” in row #1—corresponding to thefact that it least one pending packet requesting transmission via egress#2 is queued at ingress #1, an entry of “1” in row #2—corresponding tothe fact that at least one pending packet requesting transmission viaegress #2 is queued at ingress #2, and has entries of “0” in theremaining rows (e.g., row #2, and row #3)—corresponding to the fact thatno pending packets requesting transmission die egress #2 are queued ateither ingress #3, or #4.

Shown in near optimum candidates selected by schedulers diagram 1710,for sake of illustration, is a hypothetical illustration of a situationin which a first scheduler (not shown) running at egress #1 hasdetermined that its near optimum candidate for transmission is queued atingress #3, a second scheduler (not shown) running at egress #2 hasdetermined that its near optimum candidate for transmission is queued atingress #1, a third scheduler (not shown) running at egress #3 hasdetermined that its near optimum candidate for transmission is queued atingress #1, and that the fourth scheduler (not shown) running at egress#4 has determined that its near optimum candidate for transmission isqueued at ingress #2. The ingress locations of the hypothetical nearoptimal candidates for transmission associated with respective egressesare illustrated in near optimum candidates selected by schedulersdiagram 1710 by arrows running from egresses to ingresses.

Candidate Ingress Queue-Egress Physical Connections Matrix 1712illustrates in matrix form the desired ingress queue-egress physicalconnections necessary to affect the determined near optimum candidatesfor transmission shown pictographically in near optimum candidatesselected by schedulers diagram 1710. The convention utilized inCandidate Ingress Queue-Egress Physical Connections Matrix 1712 is thesimilar to that utilized in Pending Request Pattern Matrix 1708. Thatis, columns 1 through 4 correspond to egresses #1 through #4,respectively, and rows 1 through 4 correspond to ingresses #1 through#4, respectively. A “1” entered in a row and column of Candidate IngressQueue-Egress Physical Connections Matrix 1712 indicates that a candidatephysical connection exists between the egress associated with the columnand a queue at the ingress associated with the row in which the “1”appears. Notice that Candidate Ingress Queue-Egress Physical ConnectionsMatrix 1712 shows a candidate ingress #1 queue-egress #2 physicalconnection, and a candidate ingress #1 queue-egress #3 physicalconnection.

Physical connection diagram 1714 illustrates pictographicallyhypothetical granted physical connections established prior totransmission of pending packets requesting transmission illustrated innear optimum candidates selected by schedulers diagram 1712. Shown inphysical connection diagram 1714 is that a connection has beenestablished between a queue at ingress #1 and egress #2, which indicatesthat the candidate ingress #1 queue-egress #2 physical connection shownin Candidate Ingress Queue-Egress Physical Connections Matrix 1712 hasbeen granted. Depicted in physical connection diagram 1714 is that aconnection has been established between a queue at ingress #1 and egress#3, which indicates that the candidate ingress #1 queue-egress #3physical connection shown in Candidate Ingress Queue-Egress PhysicalConnections Matrix 1712 has been granted. Illustrated in physicalconnection diagram 1714 is that a connection has been establishedbetween a queue at ingress #2 and egress #4, which indicates that thecandidate ingress #2 queue-egress #4 physical connection shown inCandidate Ingress Queue-Egress Physical Connections Matrix 1712 has beengranted. Lastly, shown in physical connection diagram 1714 is that aconnection has been established between a queue at ingress #3 and egress#1, which indicates that the candidate ingress #3 queue-egress #1physical connection shown in Candidate Ingress Queue-Egress PhysicalConnections Matrix 1712 has been granted. It is to be understood thatschedulers are running substantially independently and parallel ategress #1, #2, #3, and #4 such that all connections shown in physicalconnection diagram 1714 are established substantially simultaneously.

The physical connection pattern is illustrated in matrix form viaGranted Ingress Queue-Egress Physical Connections Matrix 1716. Theconvention utilized in Granted Ingress Queue-Egress Physical ConnectionsMatrix 1716 is the same utilized in Pending Request Pattern Matrix 1708.That is, columns 1 through 4 correspond to egresses #1 through #4,respectively, and rows 1 through 4 correspond to ingresses #1 through#4, respectively. A “1” entered in a row and column of Granted IngressQueue-Egress Physical Connections Matrix 1716 indicates that a physicalconnection has been established between the respective ingressqueue-egress pair indicated by the row and column of Granted IngressQueue-Egress Physical Connections Matrix 1716.

Notice from the foregoing that the pattern composed of “1” and “0” shownin Candidate Ingress Queue-Egress Physical Connections Matrix 1712 issubstantially the same as the pattern composed of “1” and “0” shown inGranted Ingress Queue-Egress Physical Connections Matrix 1716. Thissimilarity between the two patterns arises from the fact thatcross-point buffer switch 1700 has a separate physical queue for eachingress queue-egress pair. The fact that each ingress queue-egress pairhas an independently accessible separate physical queue allows thesimultaneous physical connection of egress #2 with egress #2'srespective physical queue associated with ingress #1, and egress #3 withegress #3's respective physical queue associated with ingress #1. Thisis not possible with a input-buffered crossbar switch, which gives riseto complications, as will now be shown.

Referring now to FIG. 18, depicted is an example of a crossbar switch1800, having one input buffer 1801 per each ingress of crossbar switch1800, where each switch ingress has associated with it a number of“queues”. Crossbar switch 1800 is depicted as a 4×4 switch, having fouringresses 1804 and four egresses 1806, with each ingress-egress pairhaving associated with it a “queue” (“queue” is in quotes since the“queues” shown are not physically separate and independently accessiblequeues as denoted in cross-point switch 1700, but are rather logicalpartitions in a physical memory associated with each ingress—which meansthat only one “queue” per ingress can be physically accessed at any onetime). The “queues” shown in FIG. 18 follow the same notation as thatused in FIG. 17; that is, each queue is denoted as Q first subscriptsecond subscript where “first subscript” equates to the queue's ingressnumber and where “second subscript” equates to the queue's egressnumber.

In FIG. 18,,input buffers 1801 are shown a distance apart from crossbarswitch 1800 to make clear that only one “queue” implemented within suchbuffer can be accessed at any one time by an egress. However, it is tobe understood that crossbar switch 1800 having input buffers 1801accepts and buffers packets received over their respective ingresses1804.

Depicted in FIG. 18 is that crossbar switch 1800 having input buffers1801 is reacting to the same state of events as that shown in FIG. 17.That is, pending packets requesting transmission diagram 1802 isillustrated substantially identical to pending packets requestingtransmission diagram 1702, except for the fact that ingresses 1804 andegresses 1806 shown are for crossbar switch 1800. Consequently, PendingRequest Pattern Matrix 1808 is illustrated substantially identical toPending Request Pattern Matrix 1708, except for the fact that ingresses1804 and egresses 1806 referenced are for crossbar switch 1800. For thesake of illustration, shown also is that near optimum candidatesselected by schedulers diagram 1810 is substantially identical to nearoptimum candidates selected by schedulers diagram 1710, except for thefact that the ingresses 1804 and egresses 1806 referenced are forcrossbar switch 1800. Consequently, Candidate Ingress Queue-EgressPhysical Connections Matrix 1812 is illustrated substantially identicalto candidate ingress-egress physical connections matrix 1712, except forthe fact that ingresses 1804 and egresses 1806 referenced are forcrossbar switch 1800.

Note that even though near optimum candidates selected by schedulersdiagram 1810 is depicted substantially identical to near optimumcandidates selected by schedulers diagram 1710, and Candidate IngressQueue-Egress Physical Connections Matrix 1812 is illustratedsubstantially identical to Candidate Ingress Queue-Egress PhysicalConnections Matrix 1712, the physical constraints of crossbar switch1800 having input buffers 1801 make it physically impossible to havephysical connections such as those illustrated in physical connectiondiagram 1714, and Granted Ingress Queue-Egress Physical ConnectionsMatrix 1716, of FIG. 17. However, also note that the near optimumsituation is that such simultaneous connection would be the near optimumsituation. Thus, there is a contention between equally importantrequests for an egress port. It is necessary to resolve this contention.

Physical connection diagram 1814 illustrates pictographically asubstantially different hypothetical physical connection than that shownin physical connection diagram 1714 of FIG. 17. In physical connectiondiagram 1814 the just-discussed contention has been resolved. Physicalconnection diagram 1814 shows physical connections established prior togranting and transmission of pending packets requesting transmissionillustrated in pending packets requesting transmission diagram 1802.Shown in physical connection diagram 1814 is that a connection has beenestablished between a queue at ingress #1 and egress #2, which indicatesthat the candidate ingress #1 queue-egress #2 physical connection shownin Candidate Ingress Queue-Egress Physical Connections Matrix 1812 hasbeen granted. Depicted in physical connection diagram 1814 is that aconnection has been between a queue at ingress #2 and egress #4, whichindicates that the candidate ingress #2 queue-egress #4 physicalconnection shown in Candidate Ingress Queue-Egress Physical ConnectionsMatrix 1812 has been granted. Lastly, shown in physical connectiondiagram 1814 is that a connection has been established between a queueat ingress #3 and egress #1, which indicates that the candidate ingress#3 queue-egress #1 physical connection shown in Candidate IngressQueue-Egress Physical Connections Matrix 1812 has been granted. (It isto be understood that schedulers are running substantially independentlyand parallel at egress #1, #2, #3, and #4 such that all connectionsshown in physical connection diagram 1814 are established substantiallysimultaneously.)

The physical connection diagram 1814 is illustrated in matrix form viaGranted Ingress Queue-Egress Physical Connections Matrix 1816. Theconvention utilized in Granted Ingress Queue-Egress Physical ConnectionsMatrix 1816 is the same utilized in Granted Ingress Queue-EgressPhysical Connections Matrix 1716. That is, columns 1 through 4correspond to egresses #1 through #4, respectively, and rows 1 through 4correspond to ingresses #1 through #4, respectively. A “1” entered in arow and column of Granted Ingress Queue-Egress Physical ConnectionsMatrix 1816 indicates that a physical connection has been establishedbetween the respective ingress queue-egress pair indicated by the rowand column and thus that the corresponding candidate physical connectionbetween the corresponding ingress queue-egress pair illustrated inCandidate Ingress Queue-Egress Physical Connections Matrix 1812 has beengranted.

Notice that unlike in the physical connection diagram of FIG. 17,illustrated in Granted Ingress Queue-Egress Physical Connections Matrix1816 is that no connection has been granted between egress #3 andingress #1—the contention with respect to ingress #1 having beenresolved. Deciding how to resolve the contention between the two-equallyvaluable pending requests, while taking account of guaranteed minimumbandwidth and excess bandwidth constraints, requires a substantiallydifferent process than that described previously in relation to thecrosspoint switch. This substantially different process will now bediscussed.

In addition to the foregoing, the following described processes anddevices make use of bandwidth counters, denoted _(Wingress) _(—) _(i,)_(—) _(egress) _(—) _(e), where the bandwidth counter is associated withan ingress i and an egress e. For substantially the same reasons asthose discussed in relation to the cross-point buffer switch, above, itis important that the bandwidth counters associated with each ingressand egress be kept current. Accordingly, it is to be understood thatsubstantially simultaneous with the following described processes anddevices, processes are running at, or associated with, each egress whichreset, or reinitialize, the bandwidth counters associated with eachegress upon the expiration of a specified time interval associated witheach egress. For example, a process analogous to that shown in FIG. 7 isto be understood to be running at and associated with a first egress ofan input-buffered crossbar switch (e.g., egress #1 of input-bufferedcrossbar switch 1800), which updates the bandwidth counters associatedwith that first egress of the input-buffered crossbar switch and whichare utilized by the processes and devices described below. Likewise, aprocess analogous to that shown in FIG. 10 is to be understood to berunning at and associated with a second egress of an input bufferedcrossbar switch (e.g., egress #2 of input-buffered crossbar switch1800), which updates the bandwidth counters associated with that secondegress of the input-buffered crossbar switch and which are utilized bythe processes and devices described below. It is to be understood thatlike processes are running at all egresses described below such that thebandwidth counters associated with each such egress are reinitialized,or kept current, upon the expiration of respective time intervalsdesignated for each such egress.

With reference now to FIG. 19, shown is a high-level logic flowchartillustrating a process which can be utilized with cross bar switcheshaving input buffers. Method step 1900 illustrates the start of theprocess. Method step 1902 shows the initialization of three differentpointers: a pointer utilized to take into account guaranteed minimumbandwidth scheduler constraints for egress_e, “PE_e”, is set equal toone for all e=1 up to E, where E has the value of the highest ordinalnumber of egresses from a particular crossbar switch (e.g., E would havevalue of four for crossbar switch 1800); a pointer utilized to take intoaccount excess bandwidth scheduler constraints for Egress_e, “PEB_e”, isset equal to one for all e=1 up to E, where E has the value of thehighest ordinal number of egresses from a particular crossbar switch;and, a pointer utilized to resolve ingress contentions for ingress_i,“PI_i”, is set equal to one for all i=1 up to I, where I has a value ofthe highest ordinal number of ingresses to a particular crossbar switch(e.g., I would have value of four for crossbar switch 1800). Thereafter,method step 1904 depicts that a determination is made as to whether anyqueue associated with any switch egress has a packet waiting fortransmission; method step 1904 shows that this is achieved by checkingwhether any Queue_(Ingress) _(—) _((i)-Egress) _(—) _((e)), where i cantake on any value from 1 to I (i.e., highest ordinal number of ingressesinto switch) and where e can take on any value from 1 to E (i.e.,highest ordinal number of the egresses from switch). In the event thatno queue has a packet waiting for transmission, the process proceeds tomethod step 1906 which shows that no packet is transmitted to any port.However, in the event that at least one queue has a packet waiting fortransmission, the process proceeds to method step 1908 which shows theexecution of a “packet transmit by contention resolution and transmitpacket schedulers” process.

Referring now to FIG. 20, shown is an example of a “packet transmit bycontention resolution and transmit packet scheduler” process. Methodstep 1908A shows the start of “packet transmitted by contentionresolution and transmit packets schedulers” process. Method step 2000shows the engagement in an “schedulers (one at each egress) utilizeguaranteed minimum bandwidth and excess bandwidth constraints to resolveany contentions arising from more than one queue at the same ingressvying for access to an egress, and build Candidate Ingress Queue-EgressPhysical Connections Matrix for each egress” process, which willessentially create, or build, Candidate Ingress Queue-Egress PhysicalConnections Matrix for a particular switch in question (e.g., a matrixsuch as Candidate Ingress Queue-Egress Physical Connections Matrix 1812illustrated in FIG. 18) where the matrix built will indicate candidatephysical connections between particular ingresses and particularegresses. Thereafter, as has been shown in the example of FIG. 18, it ispossible and indeed likely that the created, or built, Candidate IngressQueue-Egress Physical Connections Matrix will have more than one ingresscontending for access to the same egress; consequently, method step 2002depicts the engagement in an “ingress queue-egress connection schedulers(one at each egress) utilize Candidate Ingress Queue-Egress PhysicalConnections Matrix, resolve any contentions arising from more than oneegress scheduled to connect to the same ingress, and build GrantedIngress Queue-Egress Physical Connections Matrix for each egress”process whereby any contentions such as those illustrated in nearoptimum candidates selected by schedulers diagram 1810 of FIG. 18 areresolved and physical connections, analogous to those illustrated inphysical connection diagram 1814 of FIG. 18, are granted.

Subsequent to the establishment of the appropriate physical connectionsnecessary to transmit the granted candidates, method step 2004 showsthat a “transmission units (one at each egress), utilizing GrantedIngress Queue-Egress Physical Connections Matrix, transmit packetsadjusting bandwidth counters as appropriate” process is engaged in.Thereafter, the process proceeds to method step 1908B which depicts theend of the “packet transmit by contention resolution and transmit packetschedulers” process.

With reference now to FIG. 21, shown is an example of the “schedulers(one at each egress) utilize guaranteed minimum bandwidth and excessbandwidth constraints to resolve any contentions arising from more thanone queue at the same ingress vying for access to an egress, and buildCandidate Ingress Queue-Egress Physical Connections Matrix for eachegress” process referenced in method step 2000. Method step 2000Adepicts the start of the example of the “schedulers (one at each egress)utilize guaranteed minimum bandwidth and excess bandwidth constraints toresolve any contentions arising from more than one queue at the sameingress vying for access to an egress, and build Candidate IngressQueue-Egress Physical Connections Matrix for each egress” processreferenced in method stop 2000. Method step 2100 shows that an EgressDesignator variable, “e”, is initialized equal to zero (0). Thereafter,method step 2102 depicts that the egress designator variable “e” isincremented by one (1).

Method step 2104 illustrates the inquiry as to whether any queueassociated with any ingress feeding the egress denoted by egressdesignator e has a packet waiting for transmission, which is illustratedas being accomplished by examining all Queue_(Ingress) _(—) _(i-Egress)_(—) _(e) where e is the current value of egress designator e and i cantake on any valid value from one to the highest ordinal number ofingresses I (e.g., in relation to the crossbar switch shown in FIG. 18,the highest ordinal number of ingresses I would be four (4), while inrelation to the crossbar switch shown in FIG. 18, the highest ordinalnumber of ingresses I would be three (3)). If the inquiry illustrated inmethod step 2104 shows that no queue associated with any ingress feedingthe egress denoted by egress designator e has a packet waiting fortransmission, the process proceeds to method step 2106 which shows theengagement in a “no candidate packet selected” process which isdiscussed in detail below but which essentially builds the column ofIngress-Egress associated with Egress_e in such a fashion that it isapparent that there are to be no candidate Ingress-Egress connectionsassociated with Egress e. Thereafter, the process proceeds to methodstep 2114.

Method step 2114 depicts the inquiry of whether e is equal to thegreatest ordinal number of egresses, E, which indicates that allegresses have been examined in which case the process proceeds to methodstep 2000B which shows the end of the example of the “schedulers (one ateach egress) utilize guaranteed minimum bandwidth and excess bandwidthconstraints to resolve any contentions arising from more than one queueat the same ingress vying for access to an egress, and build CandidateIngress Queue-Egress Physical Connections Matrix for each egress”process referenced in method stop 2000.

If the inquiry illustrated in method step 2104 shows that at least onequeue associated with any ingress feeding the egress denoted by egressdesignator e has a packet waiting for transmission, the process proceedsto method step 2108 which depicts an inquiry of whether any one ofQueue_(Ingress) _(—) _(i-Egress) _(—) _(e) associated with any ingressfeeding the egress denoted by egress designator e (i.e., Egress_e),having a packet waiting for transmission also has a non-zero bandwidthcounter. If the inquiry illustrated in method step 2108 shows that atleast one of Queue_(Ingress) _(—) _(i-Egress)_e, associated with anyingress feeding the egress denoted by egress designator e (i.e.,Egress_e), having a packet waiting for transmission also has a non-zerobandwidth counter then it is known that the potential ingress candidateselection for Egress_e must take into account guaranteed minimumbandwidth concerns for one or more ingresses associated with Egress_e,and consequently the process proceeds to method step 2110 which showsthe engagement in a “Select a Candidate for Egress_e Taking Into AccountMinimum Bandwidth Scheduler Constraints” process, discussed in moredetail below. Thereafter, the process proceeds to method step 2114 andcontinues from that point.

If the inquiry illustrated in method step 2104 shows that no queueassociated with any ingress feeding the egress denoted by egressdesignator e has a packet waiting for transmission, then it is knownthat the potential ingress candidate selection for Egress_e need nottake into account guaranteed minimum bandwidth concerns for one or moreingresses associated with Egress_e, and consequently the processproceeds to method step 2112 which shows the engagement in a “Select aCandidate for Egress_e Taking Into Account Excess Bandwidth SchedulerConstraints” process. Thereafter, the process proceeds to method step2114 and continues from that point.

Referring now to FIG. 22, depicted is an example of the “no candidatepacket selected” process referenced in method step 2106. Method step2106A illustrates the start of the example of the “no candidate packetselected” process reference in method step 2106. Method step 2200 showsthe building or construction of column e of Candidate IngressQueue-Egress Physical Connections Matrix, which is utilized to denotedthe candidate Ingress physical connection(s) associated with Egress_e,which is depicted as setting all row entries of column e of CandidateIngress Queue-Egress Physical Connections Matrix to zero (0).Thereafter, the process proceeds to method step 2106B which illustratesthe end of the example of the “no candidate packet selected” processreference in method step 2106.

With reference now to FIG. 23, illustrated is an example of the “Selecta Candidate for Egress_e Taking Into Account Minimum Bandwidth SchedulerConstraints” process referenced in method step 2110. Method step 2110Ashows the start of the example of the “Select a Candidate for Egress_eTaking Into Account Minimum Bandwidth Scheduler Constraints” processreferenced in method step 2110. Method step 2300 shows the inquiry ofwhether W_(Ingess) _(—) _((PE) _(—) _(e) _(—) ₎ _(—) _(Egress) _(—)_(e), the bandwidth counter associated with Ingress_(PE_e)_Egress_e isnon-zero (the notation used means that bandwidth counter associated withIngress 3 feeding Egress 2 if e has value equal to two (2) and pointerPE_2 contains value equal to 3). In the event that the inquiry depictedin method step 2300 shows that W_(Ingess) the bandwidth counterassociated with Ingress_(PE_e)_Egress_e is zero, it is known that theingress denoted by the value of PE_e has had its guaranteed minimumbandwidth satisfied; consequently, the process proceeds to method step2302 which shows the engagement in an “update value of PE_e” process,which is explained in more detail below, but which essentiallyincrements the value held within PE_e (note that it is the value heldwithin pointer PE_e that is being incremented—e is NOT being incrementedat this point) so that PE_e is now pointing at the next ingressassociated with Egress_e. Thereafter, the process proceeds to methodstep 2300.

In the event that the inquiry depicted in method step 2300 shows thatW_(Ingess) _(—) _((PE) _(—) _(e) _(—) ₎ _(—) _(Egress) _(—) _(e), thebandwidth counter associated with Ingress_(PE_e)_Egress_e is non-zero,it is known that the ingress denoted by the value of PE_e has NOT hadits guaranteed minimum bandwidth satisfied; consequently, the processproceeds to method step 2304 which shows the engagement in an inquiry asto whether there is actually a packet waiting for transmission in thequeue associated with Ingress_(PE_e)-Egress_e (this step is necessary inthat it is possible that one of the ingresses feeding Egress_e mightactually have a non-zero bandwidth counter but not have a packetawaiting transmission at this particular point in time). In the eventthat the inquiry depicted in method step 2304 which shows that there isno packet waiting for transmission in the queue associated withIngress_(PE_e)-Egress_e the process proceeds to method step 2302 andengages in the “update value of PE_e” process, which essentiallyincrements the value held within PE_e (note that it is the value heldwithin pointer PE_e that is being incremented—e is NOT being incrementedat this point) so that PE_e is now pointing at the next ingressassociated with Egress_e. Thereafter, the process proceeds to methodstep 2300.

In the event that the inquiry depicted in method step 2304 which showsthat there is a packet waiting for transmission in the queue associatedwith Ingress_(PE_e)-Egress_e the process proceeds to method step 2306,wherein is shown the building or construction of column e of CandidateIngress Queue-Egress Physical Connections Matrix, which is utilized todenote the candidate Ingress physical connection(s) associated withEgress_e, where such construction or building is depicted as setting therow entry PE_e of column e of Candidate Ingress Queue-Egress PhysicalConnections Matrix to one (1) to indicate that Ingress_(PE_e) is anIngress which has yet to have its access, or guaranteed minimumbandwidth requirements, with respect to Egress_e satisfied. Thereafter,the process proceeds to method step 2110B which illustrates the end ofthe example of the “Select a Candidate for Egress_e Taking Into AccountMinimum Bandwidth Scheduler Constraints” process referenced in methodstep 2110.

Notice that even though an ingress has been selected as a candidate forpossible physical connection to Egress_e, no adjustment subtraction fromthe bandwidth counter associated with the selected ingress has beendone. The reason for this is that the fact that a particularinput-buffered crossbar switch (e.g., crossbar switch 1800) can onlyconnect to one ingress at a time, so the fact that an ingress has apacket deserving of immediate transmission does not mean that the packetwill be transmitted. Whether or not it will be transmitted depends uponthe ultimate actions by a contention resolution process described below,and thus the adjustment of the bandwidth counter must be deferred untila decision is made as to which candidate connections will be made andwhich queues actually will have packets transmitted.

Referring now to FIG. 24, shown is an example of the “update value heldwithin pointer PE_e” process referenced in method step 2302. Method step2302A shows the start of the example of the “update value held withinpointer PE_e” process referenced in method step 2302. Method step 2400depicts that the value of (or held within) pointer PE_e is incrementedby one (1) (again, realize that it is the value of PE_e that is beingincremented—e is not being incremented). Thereafter, method step 2402depicts the inquiry as to whether the value of PE_e is greater than I,where I is the highest ordinal number of ingresses. In the event thatthe inquiry of method step 2402 indicates that the value of PE_e isgreater than 1, where I is the highest ordinal number of ingresses, theprocess proceeds to method step 2404 which illustrates that the value ofPE_e is set equal, or reinitialized, to one (1). Thereafter, the processproceeds to method step 2302B which shows the end of the example of the“update value held within pointer PE_e” process referenced in methodstep 2302.

With reference now to FIG. 25, depicted is an example of the “Select aCandidate for Egress_e Taking Into Account Excess Bandwidth SchedulerConstraints” process referenced in method step 2112. Method step 2112Aillustrates the start of the example the “Select a Candidate forEgress_e Taking Into Account Excess Bandwidth Scheduler Constraints”process referenced in method step 2112.

Method step 2500 shows the inquiry of whether Queue_(Ingess) _(—)_((PEB) _(—) _(e)) _(—) _(Egress) _(—) _(e) has a packet waiting fortransmission (the notation used means that the queue being examined willbe that associated with Ingress_1 feeding Egress_3 if e has value equalto three (3) and pointer PEB_3 contains value equal to one (1)). In theevent that the inquiry depicted in method step 2500 shows thatQ_(Ingess) _(—) _((PEB) _(—) _(e) _(—) ₎ _(—) _(Egress) _(—) _(e), thequeue associated with Ingress_(PEB_e)_(')Egress_e does not have a packetwaiting for transmission, the process proceeds to method step 2502 whichshows the engagement in an “update value of PEB_e” process, which isexplained in more detail below, but which essentially increments thevalue held within PEB_e (note that it is the value held within pointerPEB_e that is being incremented—e is NOT being incremented at thispoint) so that PEB_e is now pointing at the next ingress associated withEgress_e. Thereafter, the process proceeds to method step 2500.

In the event that the inquiry depicted in method step 2500 shows thatQ_(Ingess) _(—) _((PEB) _(—) _(e) _(—) ₎ _(—) _(Egress) _(—) _(e) thequeue associated with Ingress_(PE_e)_Egress_e, does have a packetwaiting for transmission, the process proceeds to method step 2504 whichshows the building or construction of column e of Candidate IngressQueue-Egress Physical Connections Matrix, which is utilized to denotethe candidate Ingress physical connection(s) associated with Egress_e,where such construction or building is depicted as setting the row entryPEB_e of column e of Candidate Ingress Queue-Egress Physical ConnectionsMatrix to one (1) to indicate that Ingress_(PEB_e) is a potentialcandidate for connection with respect to Egress_e satisfied. Thereafter,the process proceeds to method step 2112B which illustrates the end ofthe example the “Select a Candidate for Egress_e Taking Into AccountExcess Bandwidth Scheduler Go Constraints” process referenced in methodstep 2112.

Referring now to FIG. 26, shown is an example of the “update value heldwithin PEB_e” process referenced in method step 2502. Method step 2502Ashows the start of the example of the “update value held within pointerPEB_e” process referenced in method step 2502. Method step 2600 depictsthat the value of (or held within) pointer PEB_e is incremented by one(1) (again, realize that it is the value of PEB_e that is beingincremented—e is not being incremented). Thereafter, method step 2602depicts the inquiry as to whether the value of PEB_e is greater than I,where I is the highest ordinal number of ingresses. In the event thatthe inquiry of method step 2602 indicates that the value of PEB_e isgreater than I, where I is the highest ordinal number of ingresses, theprocess proceeds to method step 2604 which illustrates that the value ofPEB_e is set equal, or reinitialized, to one (1). Thereafter, theprocess proceeds to method step 2502B which shows the end of the exampleof the “update value held within pointer PEB_e” process referenced inmethod step 2502.

With reference now to FIG. 27, shown is an example of the “ingressqueue-egress connection schedulers (one at each egress) utilizeCandidate Ingress Queue-Egress Physical Connections Matrix, resolve anycontentions arising from more than one egress scheduled to connect tothe same ingress, and build Granted Ingress Queue-Egress PhysicalConnections Matrix for each egress” process referenced in method step2002. Method step 2002A depicts the start of the example of the “ingressqueue-egress connection schedulers (one at each egress) utilizeCandidate Ingress Queue-Egress Physical Connections Matrix, resolve anycontentions arising from more than one egress scheduled to connect tothe same ingress, and build Granted Ingress Queue-Egress PhysicalConnections Matrix for each egress” process referenced in method step2002. Method step 2700 illustrates that ingress designator, “i,” isinitialized equal to zero (0). Method step 2702 shows that ingressdesignator i is incremented by one (1). Method step 2704 depicts theinquiry as to whether any entry of row i of Candidate IngressQueue-Egress Physical Connections Matrix is non-zero, which isindicative of the fact that the ingress associated with row i (e.g.,Ingress_i) has a packet which needs to be preferably immediatelytransmitted over an Egress associate with Ingress_i. In the event thatthe inquiry illustrated in method step 2704 shows that at least oneentry of row i of Candidate Ingress Queue-Egress Physical ConnectionsMatrix is non-zero, it is known that the ingress associated with row i(e.g., Ingress_i) has a packet which needs to be preferably immediatelytransmitted over an Egress associated with Ingress_i. At this point,since it is known that Candidate Ingress Queue-Egress PhysicalConnections Matrix was constructed on a column-by-column basis, it isalso known that it is possible that more than one entry of row i isnon-zero, which in practical terms means that the ingress associatedwith row i of the Candidate Ingress Queue-Egress Physical ConnectionsMatrix (e.g., Ingress_i) has packets waiting for transmission indifferent queues which give rise to a need to simultaneously connect thedifferent queues at Ingress i to more than one egress. However, as hasbeen discussed, in a input-buffered crossbar switch (e.g., crossbarswitch 1800 having input buffers) such simultaneous connection of two ormore queues at one ingress with two or more egresses is not possible.Thus, this contention needs to be resolved.

One way in which this contention can be resolved is to cycle through therow entries of row i and grant the first candidate connectionencountered in a way which will now be illustrated. Method step 2708depicts the inquiry as to whether column entry PI_i of row i ofCandidate Ingress Queue-Egress Physical Connections Matrix is non-zero.If the inquiry illustrated in method step 2708 indicates that the columnentry PI_i of row i of Candidate Ingress Queue-Egress PhysicalConnections Matrix is zero, it is known that no candidate connectionwith respect to the egress associated with column PI_i of CandidateIngress Queue-Egress Physical Connections Matrix exists, and thus theprocess proceeds to method step 2710 which shows the engagement in an“update the value of PI_i” process, which will be explained in detailbelow but which essentially increments the value held within PI_i (notethat it is the value held within PI_i which is updated—it is notincremented in this step). Thereafter, the process proceeds to methodstep 2716 which shows the determination of whether i is equal to I,which is the highest ordinal number of Ingresses. In the event that theinquiry depicted in method step 2716 shows that i does equal I, theprocess proceed to method step 2002B, which shows the end of the exampleof the “ingress queue-egress connection schedulers (one at each egress)utilize Candidate Ingress Queue-Egress Physical Connections Matrix,resolve any contentions arising from more than one egress scheduled toconnect to the same ingress, and build Granted Ingress Queue-EgressPhysical Connections Matrix for each egress” process referenced inmethod step 2002.

If the inquiry illustrated in method step 2708 indicates that the columnentry PI_i of row i of Candidate Ingress Queue-Egress PhysicalConnections Matrix is non-zero, it is known that a candidate connectionwith respect to the egress associated with column PI_i of CandidateIngress Queue-Egress Physical Connections Matrix exists, and thus theprocess proceeds to method step 2712 which shows the creation, orbuilding, of row i of Granted Ingress Queue-Egress Physical ConnectionsMatrix (i.e., the row corresponding the granted physical connection withIngress_i which is associated with row i of the Candidate IngressQueue-Egress Physical Connections Matrix), which is depicted as beingachieved by setting to one (1) the row i column PI_i entry of theGranted Ingress Queue-Egress Physical Connections Matrix (where thesetting of the entry to one indicates that the candidate connectionbetween Ingress_i and Egress_(PI_i) has been granted) and setting tozero the rest of the row entries of row i where the columns do not equalPI_i (where the setting to zero of the other row entries means that anyother candidate connections for Ingress_i have been denied—thusresolving any contentions associated with Ingress_i). Thereafter, theprocess proceeds to method step 2714 which shows the engagement in an“update the value of PI_i” process, which will be explained in detailbelow but which essentially increments the value held within PI_i (notethat it is the value held within PI_i which is updated—it is notincremented in this step). Thereafter, the process proceeds to methodstep 2716.

Returning now to the inquiry of method step 2704, in the event that theinquiry illustrated in method step 2704 shows that no entry of row i ofCandidate Ingress Queue-Egress Physical Connections Matrix is non-zero,it is known that the ingress associated with row i (e.g., Ingress_i)does not have a packet which needs to be preferably immediatelytransmitted over an Egress associated with Ingress_i.

Accordingly, the process proceeds to method step 2706, which depictsthat all entries of row i of Granted Ingress Queue-Egress PhysicalConnections Matrix are set equal to zero (where the setting of the entryto zero indicates that no physical connection between Ingress_i,associated with row i, and Egress_1 through Egress_E, associated withcolumn 1 through E of the Granted physical connection matrix, has beengranted). Thereafter, the process proceeds to method step 2716 andcontinues from that point.

Subsequent to method step 2002B, it is known what candidate physicalconnections, which were illustrated by the non-zero entries containedwithin Candidate Ingress Queue-Egress Physical Connections Matrix, haveactually been granted. The actual physical connections granted are nowillustrated by the non-zero entries contained within Granted PhysicalConnections Matrix.

It was mentioned above that the adjustment of bandwidth counters had towait until contention were resolved and physical connections granted.Insofar as the foregoing has now been done, it is possible to transmitthe pending packets of the established or granted physical connections,and adjust the bandwidth counters as appropriate. These operationsreferenced in method step 2004 and will be illustrated in FIG. 29,below.

Referring now to FIG. 28, shown is an example of the “update value heldwithin PI_i” process referenced in method steps 2714 and 2710. Methodstep 2710A shows the start of the example of the “update value heldwithin PI_i” process referenced in method steps 2714 and 2710. Methodstep 2800 depicts that the value of (or held within) pointer PI_i isincremented by one (1) (again, realize that it is the value of PI_i thatis being incremented—i is not being incremented). Thereafter, methodstep 2802 depicts the inquiry as to whether the value of PI_i is greaterthan I, where I is the highest ordinal number of ingresses. In the eventthat the inquiry of method step 2802 indicates that the value of PI_i isgreater than I, where I is the highest ordinal number of ingresses, theprocess proceeds to method step 2804 which illustrates that the value ofPI_i is set equal, or reinitialized, to one (1). Thereafter, the processproceeds to method step 2710B which shows the end of the example of the“update value held within PI_i” process referenced in method steps 2714and 2710.

With reference now to the FIG. 29, shown is an example of the“transmission units (one at each egress), utilizing Granted IngressQueue-Egress Physical Connections Matrix, transmit packets adjustingbandwidth counters as appropriate” process referenced in method step2004. Method step 2004A depicts the start of the example of the“transmission units (one at each egress), utilizing Granted IngressQueue-Egress Physical Connections Matrix, transmit packets adjustingbandwidth counters as appropriate” process referenced in method step2004. Method step 2900 illustrates that egress designator e is set, orinitialized, equal to zero. Method step 2902 shows that egressdesignator e is incremented by one (1).

Method step 2904 depicts the inquiry as to whether any entry of GrantedIngress Queue-Egress Physical Connections Matrix within column e (i.e.,the column associated with Egress_e) is non-zero, which indicates that aphysical connection exists over which a packet is to be transmitted. Inthe event that the inquiry illustrated in method step 2904 shows that noentry of Granted Ingress Queue-Egress Physical Connections Matrix withincolumn e (i.e., the column associated with Egress_e) is non-zero, it isknown that no physical connection exists over which a packet is to betransmitted over Egress_e, and consequently the process proceeds tomethod step 2906 which depicts that no packet is transmitted overEgress_e. Thereafter, the process proceeds to method step 2924 whereinis illustrated that inquiry as to whether e is equal to E, the highestordinal number of egresses.

In the event that the inquiry of shown in method step 2924 indicatesthat e is equal to E, the highest ordinal number of egresses, theprocess proceeds to method step 2004B, which shows the end of theexample of the “transmission units (one at each egress), utilizingGranted Ingress Queue-Egress Physical Connections Matrix, transmitpackets adjusting bandwidth counters as appropriate” process referencedin method step 2004. However, in the event that the inquiry shown inmethod step 2924 indicates that e is not equal to E, the highest ordinalnumber of egresses, the process proceeds to method step 2902 andproceeds from that point.

Returning to the inquiry shown in method step 2904, in the event thatthe inquiry illustrated in method step 2904 shows that at least oneentry of Granted Ingress Queue-Egress Physical Connections Matrix withincolumn e (i.e., the column associated with Egress_e) is non-zero, it isknown that a physical connection exists over which a packet is to betransmitted over Egress_e, and consequently the process proceeds tomethod step 2908 which depicts that ingress designator i is set, orinitialized, equal to zero (0). Thereafter, method step 2910 illustratesthat ingress designator i is incremented by one.

Method step 2912 shows the inquiry as to whether row i, corresponding toIngress_i, and column e, corresponding to Egress_e, of Granted IngressQueue-Egress Physical Connections Matrix has a non-zero (e.g., 1) entry,in which case it is known that a physical connection has been grantedbetween Ingress_i and Egress_e. In the event that the inquiry depictedin method step 2912 shows row i, corresponding to Ingress_i, and columne, corresponding to Egress_e, of Granted Ingress Queue-Egress PhysicalConnections Matrix contain a non-zero (e.g., 1) entry, it is known thata physical connection has been granted between Ingress_i and Egress_e;accordingly, the process proceeds to method step 2914 wherein isillustrated that a packet is transmitted from Q_(Ingess) _(—)_(i-Egress) _(—) _(e). Thereafter, method step 2916 shows the inquiry asto whether the bandwidth counter, W_(Ingress) _(—) _(i) _(—) _(Egress)_(—) _(e), associated with the ingress from which the packet wastransmitted in method step 2914 is greater than zero, in which case theprocess proceeds to method step 2918 which shows that that the bandwidthcounter W_(Ingress) _(—) _(i) _(—) _(Egress) _(—) _(e), associated withthe ingress from which the packet was transmitted in method step 2914 isdecreased by a factor based on packet length (again, as was discussed inrelation to the processes applicable to cross-point buffer switchesabove, a short-cut approach can be used to adjust the bandwidth counterwhen each packet transmitted is of the same fixed length; that is, thebandwidth counter will be specified as a whole number of packets to betransmitted during the interval T and thus each time a packet istransmitted the number one (1) is merely subtracted from the bandwidthcounter). Thereafter, the process proceeds to method step 2920, whichshows the engagement in an “update the value contained in pointer PE_e”process, which was described in detail, above. Subsequently, the processproceeds to method step 2924 and proceeds from that point.

In the event that the inquiry depicted in method step 2916 shows thatthe bandwidth counter, W_(Ingress) _(—) _(i) _(—) _(Egress) _(—) _(e),associated with the ingress from which the packet was transmitted inmethod step 2914 is NOT greater than zero, the process proceeds tomethod step 2922 which shows the engagement in an “update the valuecontained in pointer PEB_e” process, which was described in detail,above. Subsequently, the process proceeds to method step 2924 andproceeds from that point.

The foregoing detailed description set forth various embodiments of thepresent invention via the use of block diagrams, flowcharts, andexamples. It will be understood as notorious by those within the artthat each block diagram component, flowchart step, and operations and/orcomponents illustrated by the use of examples can be implemented,individually and/or collectively, by a wide range of hardware, software,firmware, or any combination thereof. In one embodiment, the presentinvention is implemented via Application Specific Integrated Circuits(ASICs). However, those skilled in the art will recognize that theembodiments disclosed herein, in whole or in part, can be equivalentlyimplemented in standard Integrated Circuits, as a computer programrunning on a computer, as firmware, or as virtually any combinationthereof and that designing the circuitry and/or writing the code for thesoftware or firmware would be well within the skill of one of ordinaryskill in the art in light of this disclosure. In addition, those skilledin the art will appreciate that the mechanisms of the present inventionare capable of being distributed as a program product in a variety offorms, and that an illustrative embodiment of the present inventionapplies equally regardless of the particular type of signal bearingmedia used to actually carry out the distribution. Examples of a signalbearing media include but are not limited to the following: recordabletype media such as floppy disks, hard disk drives, CD ROMs, digitaltape, and transmission type media such as digital and analoguecommunication links.

While particular embodiments of the present invention have been shownand described, it will be obvious to those skilled in the art that,based upon the teachings herein, changes and modifications may be madewithout departing from this invention and its broader aspects and,therefore, the appended claims are to encompass within their scope allsuch changes and modifications as are within the true spirit and scopeof this invention. Furthermore, it is to be understood that theinvention is solely defined by the appended claims. It will beunderstood by those within the art that if a specific number of anintroduced claim element is intended, such an intent will be explicitlyrecited in the claim, and in the absence of such recitation no suchlimitation is present. For non-limiting example, as an aid tounderstanding, the following appended claims contain usage of theintroductory phrases “at least one” and “one or more” to introduce claimelements. However, the use of such phrases should not be construed toimply that the introduction of a claim element by the indefinitearticles “a” or “an” limits any particular claim containing suchintroduced claim element to inventions containing only one such element,even when same claim includes the introductory phrases “one or more” or“at least one” and indefinite articles such as “a” or “an”; the sameholds true for the use of definite articles.

What is claimed is:
 1. A method comprising: designating a target minimumamount of actual data transmission per unit time from at least oneinput-buffered crossbar switch ingress to at least one input-bufferedcrossbar switch egress; and substantially ensuring that the targetminimum amount of actual data transmission per unit time from the atleast one input-buffered crossbar switch ingress to the at least oneinput-buffered crossbar switch egress is substantially satisfied byallowing substantially only the at least one input-buffered crossbarswitch ingress access to the at least one input-buffered crossbar switchegress when (a) the at least one input-buffered crossbar switch ingresshas data to transmit and (b) the actual data transmission per unit timefrom the least one input-buffered crossbar switch ingress to the atleast one input-buffered crossbar switch egress does not substantiallysatisfy the target minimum amount of actual data transmission per unittime from the at least one input-buffered crossbar switch ingress to theat least one input-buffered crossbar switch egress.
 2. The method ofclaim 1, wherein said allowing substantially only the at least oneinput-buffered crossbar switch ingress access to the at least oneinput-buffered crossbar switch egress when (a) the at least oneinput-buffered crossbar switch ingress has data to transmit and (b) theactual data transmission per unit time from the least one input-bufferedcrossbar switch ingress to the at least one input-buffered crossbarswitch egress does not substantially satisfy the target minimum amountof actual data transmission per unit time from the at least oneinput-buffered crossbar switch ingress to the at least oneinput-buffered crossbar switch egress further comprises: designating oneor more candidate electrical connections between one or moreinput-buffered crossbar switch egresses and one or more cross-connectswitch ingresses, taking into account the one or more cross-connectswitch ingresses' target minimum amounts of actual data transmission perunit time from the one or more input-buffered crossbar switch ingressesto the one or more input-buffered crossbar switch egresses; establishingat least one of the designated one or more candidate electricalconnections between the one or more input-buffered crossbar switchegresses and the one or more input-buffered crossbar switch ingresses;and transmitting data over the established at least one of thedesignated one or more candidate electrical connections between the oneor more input-buffered crossbar switch egresses and the one or moreinput-buffered crossbar switch ingresses.
 3. The method of claim 2,where said designating one or more candidate electrical connectionsbetween one or more input-buffered crossbar switch egresses and one ormore cross-connect switch ingresses, taking into account the one or morecross-connect switch ingresses' target minimum amounts of actual datatransmission per unit time from the one or more input-buffered crossbarswitch ingresses to the one or more input-buffered crossbar switchegresses further comprises: specifying a set of one or moreinput-buffered crossbar switch egresses; specifying a set of one or moreinput-buffered crossbar switch ingresses where each of the one or morecross-connect ingresses has a designated target minimum amount of actualdata transmission per unit time from the input-buffered crossbar switchingress to each of the one or more input-buffered crossbar switchegresses; selecting an input-buffered crossbar switch egress from theset of cross-connect switch egresses, where said selected input-bufferedcrossbar switch egress has not been previously selected; detectingwhether at least one of the one or more one input-buffered crossbarswitch ingresses has at least one packet pending transmission to theselected input-buffered crossbar switch egress; in response to saiddetecting showing that at least one of the one or more oneinput-buffered crossbar switch ingresses has at least one packet pendingtransmission to the selected input-buffered crossbar switch egress,ascertaining whether at least one of the one or more one input-bufferedcrossbar switch ingresses (a) has at least one packet pendingtransmission to the selected input-buffered crossbar switch egress and(b) has a substantially unsatisfied target minimum amount of actual datatransmission per unit time from the at least one input-buffered crossbarswitch ingress to the selected input-buffered crossbar switch egress;and in response to said ascertaining showing that at least one of theone or more one input-buffered crossbar switch ingresses (a) has atleast one packet pending transmission to the selected input-bufferedcrossbar switch egress and (b) has a substantially unsatisfied targetminimum amount of data transmission per unit time from the at least oneinput-buffered crossbar switch ingress to the selected input-bufferedcrossbar switch egress, selecting at least one candidate electricalconnection for the selected cross connect-switch egress taking accountof minimum bandwidth scheduler constraints.
 4. The method of claim 3,wherein said selecting at least one candidate electrical connection forthe selected cross connect-switch egress taking account of minimbandwidth scheduler constraints further comprises: selecting a candidateelectrical connection between an input-buffered crossbar switch ingresswhich has a packet pending transmission to the selected input-bufferedcrossbar switch egress as a candidate for electrical connection with theselected input-buffered crossbar switch egress.
 5. The method of claim4, wherein said selecting a candidate electrical connection between aninput-buffered crossbar switch ingress which has a packet pendingtransmission to the selected input-buffered crossbar switch egress as acandidate for electrical connection with the selected input-bufferedcrossbar switch egress further comprises: resolving any contentionsarising from different input-buffered switch ingresses vying for accessto the selected input-buffered switch egress.
 6. The method of claim 5,wherein said resolving any contentions arising from differentinput-buffered switch egresses vying for access to the selectedinput-buffered switch egress further comprises: examining in a definedsequence each of the one or more input-buffered crossbar switchingresses until an input-buffered crossbar switch ingress is encounteredwhich has a packet pending transmission to the selected input-bufferedcrossbar switch egress; and recording a potential connection between theencountered input-buffered crossbar switch ingress which has a packetpending transmission to the selected input-buffered crossbar switchegress as the candidate electrical connection.
 7. The method of claim 6,wherein said recording a potential connection between the encounteredinput-buffered crossbar switch ingress which has a packet pendingtransmission to the selected input-buffered crossbar switch egress asthe candidate electrical connection further comprises: building acolumn, corresponding to the selected input-buffered crossbar switchegress, in a Candidate Ingress Queue-Egress Physical Connections Matrixwhere a row entry, corresponding to the encountered input-bufferedcrossbar switch ingress which has a packet pending transmission to theselected input-buffered crossbar switch egress, is set to be non-zero.8. The method of claim 3, further comprising: in response to saidascertaining failing to show that at least one of the one or more oneinput-buffered crossbar switch ingresses (a) has at least one packetpending transmission to the selected input-buffered crossbar switchegress and (b) has a substantially unsatisfied target minimum amount ofactual data transmission per unit time from the at least oneinput-buffered crossbar switch ingress to the selected input-bufferedcrossbar switch egress, selecting at least one candidate electricalconnection for the selected cross connect-switch egress taking accountof excess bandwidth scheduler constraints.
 9. The method of claim 8,wherein said selecting at least one candidate electrical connection forthe selected cross connect-switch egress taking account of excessbandwidth scheduler constraints further comprising: selecting acandidate electrical connection between an input-buffered crossbarswitch ingress which has a packet pending transmission to the selectedinput-buffered crossbar switch egress as a candidate for electricalconnection with the selected input-buffered crossbar switch egress. 10.The method of claim 8, wherein said selecting a candidate electricalconnection between an input-buffered crossbar switch ingress which has apacket pending transmission to the selected input-buffered crossbarswitch egress as a candidate for electrical connection with the selectedinput-buffered crossbar switch egress further includes: resolving anycontentions arising from different input-buffered switch ingresses vyingfor access to the selected input-buffered switch egress.
 11. The methodof claim 10, wherein said resolving any contentions arising fromdifferent input-buffered switch egresses vying for access to theselected input-buffered switch egress further includes: examining in adefined sequence each of the one or more input-buffered crossbar switchingresses until an input-buffered crossbar switch ingress is encounteredwhich has a packet pending transmission to the selected input-bufferedcrossbar switch egress; and recording a potential connection between theencountered input-buffered crossbar switch ingress which has a packetpending transmission to the selected input-buffered crossbar switchegress as the candidate electrical connection.
 12. The method of claim11, wherein said recording a potential connection between theencountered input-buffered crossbar switch ingress which has a packetpending transmission to the selected input-buffered crossbar switchegress as the candidate electrical connection further comprises:building a column, corresponding to the selected input-buffered crossbarswitch egress, in a Candidate Ingress Queue-Egress Physical ConnectionsMatrix where a row entry, corresponding to the encounteredinput-buffered crossbar switch ingress which has a packet pendingtransmission to the selected input-buffered crossbar switch egress, isset to be non-zero.
 13. The method of claim 3, further comprising: inresponse to said detecting showing that none of the one or more oneinput-buffered crossbar switch ingresses has at least one packet pendingtransmission to the selected input-buffered crossbar switch egress,recording that none of the one or more one input-buffered crossbarswitch ingresses has at least one packet pending transmission to theselected input-buffered crossbar switch egress.
 14. The method of claim13, wherein said recording that none of the one or more oneinput-buffered crossbar switch ingresses has at least one packet pendingtransmission to the selected input-buffered crossbar switch egressfurther comprises: building a column, corresponding to the selectedinput-buffered crossbar switch egress, in a Candidate IngressQueue-Egress Physical Connections Matrix, where all row entries,corresponding to all of the one or more input-buffered crossbar switch,are set to be zero.
 15. The method of claim 3 further comprising:repeating said selecting, determining, establishing, and transmittingoperations until all of the one or more input-buffered crossbar switchegresses have been selected.
 16. The method of claim 2, wherein saidestablishing at least one of the determined one or more candidateelectrical connections between one or more input-buffered crossbarswitch egresses and one or more cross-connect switch ingresses furthercomprises: resolving any contentions arising from the existence of oneor more candidate electrical connections between differentinput-buffered switch egresses and a same input-buffered ingress; and inresponse to said resolving, establishing at least one electricalconnection between at least one of the different input buffered switchegresses and the same input-buffered crossbar switch ingress.
 17. Themethod of claim 16, wherein said resolving any contentions arising fromthe existence of one or more candidate electrical connections betweendifferent input-buffered switch egresses and a same input-bufferedcrossbar switch ingress further comprises: examining in a definedsequence each of the one or more input-buffered crossbar switch egressesuntil a candidate electrical connection between one of the differentinput-buffered crosses bar switch egresses and the same input-bufferedcrossbar switch ingress is encountered; and eliminating any othercandidate electrical connections for the same input-buffered crossbarswitch ingress.
 18. The method of claim 17, wherein said eliminating anyother candidate electrical connections for the selected input-bufferedcrossbar switch ingress further comprises: building a row, correspondingto the same input-buffered crossbar switch ingress, in a Granted IngressQueue-Egress Physical Connections Matrix where a row entry,corresponding to the encountered candidate electrical connection for thesame input-buffered cross bar switch ingress, is set to be non-zero. 19.The method of claim 2, wherein said transmitting data over theestablished at least one of the designated one or more candidateelectrical connections between the one or more input-buffered crossbarswitch egresses and the one or more input-buffered crossbar switchingresses further comprises: transmitting data over the established atleast one of the designated one or more candidate electricalconnections; recording an amount of data transmitted from aninput-buffered crossbar switch ingress to an input-buffered crossbarswitch egress forming the established at least one of the designated oneor more candidate electrical connections when a comparison shows that atarget minimum amount of actual data transmission from theinput-buffered crossbar switch ingress to the input-buffered crossbarswitch egress forming the established at least one of the designated oneor more candidate electrical connections has not been substantially met.20. The method of claim 19, wherein the comparison further comprises:adjusting a bandwidth counter indicative of a relation between theactual data transmission per unit time and the target minimum amount ofactual data transmission per unit time from the input-buffered crossbarswitch ingress to the input-buffered crossbar switch egress forming theestablished at least one of the designated one or more candidateelectrical connections; and comparing the bandwidth counter to athreshold value.
 21. The method of claim 20, wherein said adjusting abandwidth counter indicative of a relation between the actual datatransmission per unit time and the target minimum amount of actual datatransmission per unit time from the input-buffered crossbar switchingress to the input-buffered crossbar switch egress forming theestablished at least one of the designated one or more candidateelectrical connections further comprises: detecting transmission of datafrom the input-buffered crossbar switch ingress to the input-bufferedcrossbar switch egress forming the established at least one of thedesignated one or more candidate electrical connections; and in responseto said detecting, reducing the bandwidth counter by a factor dependentupon the detected transmission of data.
 22. The method of claim 21,wherein said reducing the bandwidth counter by a factor dependent uponthe detected transmission of data further comprises: reducing thebandwidth counter by a variable number when the detected transmission ofdata is based on variable-length packets.
 23. The method of claim 21,wherein said reducing the bandwidth counter by a factor dependent uponthe detected transmission of data further comprises: reducing thebandwidth counter by an integer number when the detected transmission ofdata is based on fixed-length packets.
 24. The method of claim 19,wherein said step of transmitting data over the established at least oneof the determined one or more candidate electrical connections:transmitting data over established physical connections indicated bynon-zero column entries of a Granted Ingress-Queue Egress PhysicalConnections Matrix.
 25. A system comprising: means for designating atarget minimum amount of actual data transmission per unit time from atleast one input-buffered crossbar switch ingress to at least oneinput-buffered crossbar switch egress; and means for substantiallyensuring that the target minimum amount of actual data transmission perunit time from the at least one input-buffered crossbar switch ingressto the at least one input-buffered crossbar switch egress issubstantially satisfied, said means for substantially ensuring furthercomprising: means for allowing substantially only the at least oneinput-buffered crossbar switch ingress access to the at least oneinput-buffered crossbar switch egress when (a) the at least oneinput-buffered crossbar switch ingress has data to transmit and (b) theactual data transmission per unit time from the least one input-bufferedcrossbar switch ingress to the at least one input-buffered crossbarswitch egress does not substantially satisfy the target minimum amountof actual data transmission per unit time from the at least oneinput-buffered crossbar switch ingress to the at least oneinput-buffered crossbar switch egress.
 26. The system of claim 25,wherein said means for allowing substantially only the at least oneinput-buffered crossbar switch ingress access to the at least oneinput-buffered crossbar switch egress when (a) the at least oneinput-buffered crossbar switch ingress has data to transmit and (b) theactual data transmission per unit time from the least one input-bufferedcrossbar switch ingress to the at least one input-buffered crossbarswitch egress does not substantially satisfy the target minimum amountof actual data transmission per unit time from the at least oneinput-buffered crossbar switch ingress to the at least oneinput-buffered crossbar switch egress further comprises: means fordesignating one or more candidate electrical connections between one ormore input-buffered crossbar switch egresses and one or morecross-connect switch ingresses, taking into account the one or morecross-connect switch ingresses' target minimum amounts of actual datatransmission per unit time from the one or more input-buffered crossbarswitch ingresses to the one or more input-buffered crossbar switchegresses; means for establishing at least one of the designated one ormore candidate electrical connections between the one or moreinput-buffered crossbar switch egresses and the one or moreinput-buffered crossbar switch ingresses; and means for transmittingdata over the established at least one of the designated one or morecandidate electrical connections between the one or more input-bufferedcrossbar switch egresses and the one or more input-buffered crossbarswitch ingresses.
 27. The system of claim 26, wherein said means fordesignating one or more candidate electrical connections between one ormore input-buffered crossbar switch egresses and one or morecross-connect switch ingresses, taking into account the one or morecross-connect switch ingresses' target minimum amounts of actual datatransmission per unit time from the one or more input-buffered crossbarswitch ingresses to the one or more input-buffered crossbar switchegresses further comprises: means for specifying a set of one or moreinput-buffered crossbar switch egresses; means for specifying a set ofone or more input-buffered crossbar switch ingresses where each of theone or more cross-connect ingresses has a designated target minimumamount of actual data transmission per unit time from the input-bufferedcrossbar switch ingress to each of the one or more input-bufferedcrossbar switch egresses; means for selecting an input-buffered crossbarswitch egress from the set of cross-connect switch egresses, where saidselected input-buffered crossbar switch egress has not been previouslyselected; means for detecting whether at least one of the one or moreone input-buffered crossbar switch ingresses has at least one packetpending transmission to the selected input-buffered crossbar switchegress; means, responsive to said means for detecting showing that atleast one of the one or more one input-buffered crossbar switchingresses has at least one packet pending transmission to the selectedinput-buffered crossbar switch egress, for ascertaining whether at leastone of the one or more one input-buffered crossbar switch ingresses (a)has at least one packet pending transmission to the selectedinput-buffered crossbar switch egress and (b) has a substantiallyunsatisfied target minimum amount of actual data transmission per unittime from the at least one input-buffered crossbar switch ingress to theselected input-buffered crossbar switch egress; and means, responsive tosaid means for ascertaining showing that at least one of the one or moreone input-buffered crossbar switch ingresses (a) has at least one packetpending transmission to the selected input-buffered crossbar switchegress and (b) has a substantially unsatisfied target minimum amount ofdata transmission per unit time from the at least one input-bufferedcrossbar switch ingress to the selected input-buffered crossbar switchegress, for selecting at least one candidate electrical connection forthe selected cross connect-switch egress taking account of minimumbandwidth scheduler constraints.
 28. The system of claim 27, whereinsaid means for selecting at least one candidate electrical connectionfor the selected cross connect-switch egress taking account of minimbandwidth scheduler constraints further comprises: means for selecting acandidate electrical connection between an input-buffered crossbarswitch ingress which has a packet pending transmission to the selectedinput-buffered crossbar switch egress as a candidate for electricalconnection with the selected input-buffered crossbar switch egress. 29.The system of claim 28, wherein said means for selecting a candidateelectrical connection between an input-buffered crossbar switch ingresswhich has a packet pending transmission to the selected input-bufferedcrossbar switch egress as a candidate for electrical connection with theselected input-buffered crossbar switch egress further comprises: meansfor resolving any contentions arising from different input-bufferedswitch ingresses vying for access to the selected input-buffered switchegress.
 30. The system of claim 29, wherein said means for resolving anycontentions arising from different input-buffered switch egresses vyingfor access to the selected input-buffered switch egress furthercomprises: means for examining in a defined sequence each of the one ormore input-buffered crossbar switch ingresses until an input-bufferedcrossbar switch ingress is encountered which has a packet pendingtransmission to the selected input-buffered crossbar switch egress; andmeans for recording a potential connection between the encounteredinput-buffered crossbar switch ingress which has a packet pendingtransmission to the selected input-buffered crossbar switch egress asthe candidate electrical connection.
 31. The system of claim 30, whereinsaid means for recording a potential connection between the encounteredinput-buffered crossbar switch ingress which has a packet pendingtransmission to the selected input-buffered crossbar switch egress asthe candidate electrical connection further comprises: means forbuilding a column, corresponding to the selected input-buffered crossbarswitch egress, in a Candidate Ingress Queue-Egress Physical ConnectionsMatrix where a row entry, corresponding to the encounteredinput-buffered crossbar switch ingress which has a packet pendingtransmission to the selected input-buffered crossbar switch egress, isset to be non-zero.
 32. The system of claim 27, further comprising:means, responsive to said means for ascertaining failing to show that atleast one of the one or more one input-buffered crossbar switchingresses (a) has at least one packet pending transmission to theselected input-buffered crossbar switch egress and (b) has asubstantially unsatisfied target minimum amount of actual datatransmission per unit time from the at least one input-buffered crossbarswitch ingress to the selected input-buffered crossbar switch egress,for selecting at least one candidate electrical connection for theselected cross connect-switch egress taking account of excess bandwidthscheduler constraints.
 33. The system of claim 32, wherein said meansfor selecting at least one candidate electrical connection for theselected cross connect-switch egress taking account of excess bandwidthscheduler constraints further comprising: means for selecting acandidate electrical connection between an input-buffered crossbarswitch ingress which has a packet pending transmission to the selectedinput-buffered crossbar switch egress as a candidate for electricalconnection with the selected input-buffered crossbar switch egress. 34.The system of claim 32, wherein said means for selecting a candidateelectrical connection between an input-buffered crossbar switch ingresswhich has a packet pending transmission to the selected input-bufferedcrossbar switch egress as a candidate for electrical connection with theselected input-buffered crossbar switch egress further includes: meansfor resolving any contentions arising from different input-bufferedswitch ingresses vying for access to the selected input-buffered switchegress.
 35. The system of claim 34, wherein said means for resolving anycontentions arising from different input-buffered switch egresses vyingfor access to the selected input-buffered switch egress furtherincludes: means for examining in a defined sequence each of the one ormore input-buffered crossbar switch ingresses until an input-bufferedcrossbar switch ingress is encountered which has a packet pendingtransmission to the selected input-buffered crossbar switch egress; andmeans for recording a potential connection between the encounteredinput-buffered crossbar switch ingress which has a packet pendingtransmission to the selected input-buffered crossbar switch egress asthe candidate electrical connection.
 36. The system of claim 35, whereinsaid means for recording a potential connection between the encounteredinput-buffered crossbar switch ingress which has a packet pendingtransmission to the selected input-buffered crossbar switch egress asthe candidate electrical connection further comprises: means forbuilding a column, corresponding to the selected input-buffered crossbarswitch egress, in a Candidate Ingress Queue-Egress Physical ConnectionsMatrix where a row entry, corresponding to the encounteredinput-buffered crossbar switch ingress which has a packet pendingtransmission to the selected input-buffered crossbar switch egress, isset to be non-zero.
 37. The system of claim 27, further comprising:means, responsive to said means for detecting showing that none of theone or more one input-buffered crossbar switch ingresses has at leastone packet pending transmission to the selected input-buffered crossbarswitch egress, for recording that none of the one or more oneinput-buffered crossbar switch ingresses has at least one packet pendingtransmission to the selected input-buffered crossbar switch egress. 38.The system of claim 37, wherein said means for recording that none ofthe one or more one input-buffered crossbar switch ingresses has atleast one packet pending transmission to the selected input-bufferedcrossbar switch egress further comprises: means for building a column,corresponding to the selected input-buffered crossbar switch egress, ina Candidate Ingress Queue-Egress Physical Connections Matrix, where allrow entries, corresponding to all of the one or more input-bufferedcrossbar switch, are set to be zero.
 39. The system of claim 27 furthercomprising: means for repeating said selecting, determining,establishing, and transmitting operations until all of the one or moreinput-buffered crossbar switch egresses have been selected.
 40. Thesystem of claim 26, wherein said means for establishing at least one ofthe determined one or more candidate electrical connections between oneor more input-buffered crossbar switch egresses and one or morecross-connect switch ingresses further comprises: means for resolvingany contentions arising from the existence of one or more candidateelectrical connections between different input-buffered switch egressesand a same input-buffered ingress; and means, responsive to said meansfor resolving, establishing at least one electrical connection betweenat least one of the different input buffered switch egresses and thesame input-buffered crossbar switch ingress.
 41. The system of claim 40,wherein said means for resolving any contentions arising from theexistence of one or more candidate electrical connections betweendifferent input-buffered switch egresses and a same input-bufferedcrossbar switch ingress further comprises: means for examining in adefined sequence each of the one or more input-buffered crossbar switchegresses until a candidate electrical connection between one of thedifferent input-buffered crosses bar switch egresses and the sameinput-buffered crossbar switch ingress is encountered; and means foreliminating any other candidate electrical connections for the sameinput-buffered crossbar switch ingress.
 42. The system of claim 41,where said means for eliminating any other candidate electricalconnections for the selected input-buffered crossbar switch ingressfurther comprises: means for building a row, corresponding to the sameinput-buffered crossbar switch ingress, in a Granted IngressQueue-Egress Physical Connections Matrix where a row entry,corresponding to the encountered candidate electrical connection for thesame input-buffered cross bar switch ingress, is set to be non-zero. 43.The system of claim 26, wherein said means for transmitting data overthe established at least one of the designated one or more candidateelectrical connections between the one or more input-buffered crossbarswitch egresses and the one or more input-buffered crossbar switchingresses further comprises: means for transmitting data over theestablished at least one of the designated one or more candidateelectrical connections; means for recording an amount of datatransmitted from an input-buffered crossbar switch ingress to aninput-buffered crossbar switch egress forming the established at leastone of the designated one or more candidate electrical connections whena comparison shows that a target minimum amount of actual datatransmission from the input-buffered crossbar switch ingress to theinput-buffered crossbar switch egress forming the established at leastone of the designated one or more candidate electrical connections hasnot been substantially met.
 44. The system of claim 43, wherein saidmeans for recording an amount of data transmitted from an input-bufferedcrossbar switch ingress to an input-buffered crossbar switch egressforming the established at least one of the designated one or morecandidate electrical connections when a comparison shows that a targetminimum amount of actual data transmission from the input-bufferedcrossbar switch ingress to the input-buffered crossbar switch egressforming the established at least one of the designated one or morecandidate electrical connections has not been substantially met furthercomprises: means for adjusting a bandwidth counter indicative of arelation between the actual data transmission per unit time and thetarget minimum amount of actual data transmission per unit time from theinput-buffered crossbar switch ingress to the input-buffered crossbarswitch egress forming the established at least one of the designated oneor more candidate electrical connections; and means for comparing thebandwidth counter to a threshold value.
 45. The system of claim 44,wherein said means for adjusting a bandwidth counter indicative of arelation between the actual data transmission per unit time and thetarget minimum amount of actual data transmission per unit time from theinput-buffered crossbar switch ingress to the input-buffered crossbarswitch egress forming the established at least one of the designated oneor more candidate electrical connections further comprises: means fordetecting transmission of data from the input-buffered crossbar switchingress to the input-buffered crossbar switch egress forming theestablished at least one of the designated one or more candidateelectrical connections; and means, responsive to said means fordetecting, reducing the bandwidth counter by a factor dependent upon thedetected transmission of data.
 46. The system of claim 45, wherein saidmeans for reducing the bandwidth counter by a factor dependent upon thedetected transmission of data further comprises: means for reducing thebandwidth counter by a variable number when the detected transmission ofdata is based on variable-length packets.
 47. The system of claim 45,wherein said means for reducing the bandwidth counter by a factordependent upon the detected transmission of data further comprises:means for reducing the bandwidth counter by an integer number when thedetected transmission of data is based on fixed-length packets.
 48. Thesystem of claim 43, wherein said means for transmitting data over theestablished at least one of the determined one or more candidateelectrical connections: means for transmitting data over establishedphysical connections indicated by non-zero column entries of a GrantedIngress-Queue Egress Physical Connections Matrix.
 49. The system ofclaim 25, wherein the system is a program product and wherein theprogram product further comprises: signal bearing media bearing saidmeans for designating a target minimum amount of actual datatransmission per unit time from at least one input-buffered crossbarswitch ingress to at least one input-buffered crossbar switch egress,and said means for substantially ensuring that the target minimum amountof actual data transmission per unit time from the at least oneinput-buffered crossbar switch ingress to the at least oneinput-buffered crossbar switch egress is substantially satisfied. 50.The system of claim 49, wherein said signal bearing media furthercomprises: recordable media.
 51. The system of claim 49, wherein saidsignal bearing media further comprises: transmission media.